Notes Cognitive Neuroscience
The Structure of Neurons
- nervous system is composed of two main classes of cells: neurons and
glial cells
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Neurons (100 billion / 10^11)
- neurons are the basic signaling units that transmit information
throughout the nervous system
- neurons take in information, make a “decision” about it following some
relatively simple rules, and then, by changes in their activity levels, pass it
along to other neurons
- vary in their form, location, and inter- connectivity within the nervous
system (Figure 2.2), and these variations are closely related to their
functions
- standard cellular components found in almost all eukaryotic cells are
found in neurons as well
- neuron is composed of three main parts: a cell body, dendrites, and an
axon
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cell body contains the cellular machinery for the production
of proteins and other cellular macromolecules
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dendrites and axon are extensions of the cell membrane and
contain cytoplasm continuous with that in the cell body
the neuron contains a nucleus, endoplasmic reticulum, ribosomes, mitochondria, Golgi apparatus, and other
intracellular organelles
cell membrane encases the cell body (also called soma)
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contains the metabolic machinery that maintains the neuron (nucleus, endoplasmic reticulum etc.)
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these structures are suspended in cytoplasm
§
salty intracellular fluid that is made up of a combination of ions, predominantly ions of
potassium, sodium, chloride, and calcium, as well as molecules such as proteins
neuron sits in a bath of salty extracellular fluid, which is also made up of a mixture of the same types of ions
possess unique cytological features and physiological properties that enable them to transmit and process
information rapidly
Dendrites
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branching extensions of the neuron that receive inputs from other neurons
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take many varied and complex forms, depending on the type and location of the neuron
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have specialized processes called spines
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little knobs attached by small necks to the surface of the dendrites
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where the dendrites receive inputs from other neurons
Axons
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a single output structure that extends from the axon hillock at the base of the cell soma, away from the
cell body
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Electrical signals travel down the axon toward the axon terminals, where the neuron transmits the signal
to other neurons or other cell types (via dendrites and other axons)
Axon Hillock
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Is a specialized part of the cell body that is the connection to the axon
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The last site in the cell body where membrane potentials propagated from synaptic inputs are summated
before being transmitted to the axon
Sagittal section through a cerebellar
cortex showing a Purkinje cell
Neurons located in the ventral horn
of the spinal cord send their axons
out the ventral root to make
synapses on muscle fibers
Glial Cells (1 trillion / 10^12)
nonneural cells that serve various functions in the nervous system
include providing structural support and electrical insulation to neurons, and modulating neuronal activity
roughly as many glial cells in the brain as there are neurons
Located throughout the nervous system, they may ac- count for more than half of the brain’s volume
provide structural support
helping to form the blood–brain barrier and aiding in the speed of information transfer
have a previously unrecognized role in modulating neural
activity
are also the myelin formers in the nervous system
central nervous system has three main types of glial cells:
astrocytes, microglial cells, and oligodendrocytes
Astrocytes
large glial cells with round or radially symmetrical forms
surround neurons and are in close contact with the brain’s
vasculature
makes contact with blood vessels at specializations called end
feet (permit the astrocyte to trans- port ions across the vascular
wall)
create a barrier, called the blood–brain barrier (BBB), between
the tissues of the central nervous system and the blood
restricts passing of most bacteria, large hydrophilic molecules in
the blood in the neural tissue
allows small hydrophobic molecules such as oxygen, carbon
dioxide, and hormones to enter
active role in brain function
Microglial Cells
small and irregularly shaped
come into play when tissue is damaged
devouring and removing damaged cells
can proliferate even in adults
Oligodendrocytes and Schwann cells
in the central nervous system, oligodendrocytes form myelin
in the peripheral nervous system, Schwann cells form myelin
create myelin by wrapping their cell membranes around the axon in a
concentric manner during development and maturation
cytoplasm in that portion of the glial cell is squeezed out
leaving primarily the lipid bilayer of the glial cell sheathing the membrane
Key Points the Structure of Neurons:
Neurons and glial cells make up the nervous system.
Neurons are the cells that transmit information
throughout the nervous system. Most neurons consist of a
cell soma (body), axon, and dendrites.
Neurons communicate with other neurons and cells at
specialized structures called synapses, where chemical and
electrical signals can be conveyed between neurons.
An astrocyte is a type of glial cell that helps form the
blood–brain barrier.
Astrocytes have an active role in modulating neural
activity.
Glial cells aid in the speed of information transfer by
forming myelin around the axons of the neurons.
An oligodendrocyte is a type of glial cell that forms myelin
in the central nervous system.
A Schwann cell is a type of glial cell that forms myelin in
the peripheral nervous system.
As part of the immune response of the nervous system,
microglial cells are phagocytic cells that engulf damaged
cells.
Myelin is a good electrical insulator
because the layers of cell membrane are
composed of lipid bilayers, which are
themselves poor electrical conductors
Neuronal Signaling
- Neurons receive, evaluate, and transmit information
- Two types of transportation
- Information is transferred across synapses from one neuron to the next,
or from a neuron to a non-neuronal cell such as those in muscles or glands
- being received at synapses on dendrites, conducted with- in the neuron,
transmitted down the axon, and passed along at synapses on the axon
terminals
- Within a neuron, transferring information involves changes in the
electrical state of the neuron as electrical currents flow through the
volume of the neuron
- Between neurons, information transfer occurs at synapses, typically
mediated by chemical signaling molecules (neurotransmitters) but, in
some cases, also by electrical signals
- Regarding information flow, neurons are referred to as either
presynaptic or postsynaptic in relation to any particular synapse
- Most neurons are both presynaptic and postsynaptic
Presynaptic
- A neuron is presynaptic when their axon makes a connection onto other
neurons
Postsynaptic
A neuron is postsynaptic when other neurons make a connection onto their dendrites
The Membrane Potential
process of signaling has several stages
energy is needed to generate the signals
this energy is in the form of an electrical potential
across the neuronal membrane
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electrical potential is the voltage inside
the neuron versus out- side the neuron
these two voltages depend on the concentrations
of potassium, sodium, and chloride ions as well as
on charged protein molecules both inside and
outside of the cell
voltage difference across the neuronal membrane
in the resting state is typically −70 millivolts (mV)
inside (known as resting membrane potential)
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means that the neuron has at its
disposal a kind of battery
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stored energy can be used to do work
lipid membrane maintains the separation of
intracellular and extracellular ions and electrical
charge that ultimately permits neuronal
communication
membrane is peppered with transmembrane
proteins that serve as conduits for ions to move
across the neuronal membrane
two main types of these proteins: ion channels
and ion pumps
Ion Channels
proteins with a pore through their centers
they allow certain ions to flow down their concentration gradients
transmembrane passageways created by ion channels are formed from the three-dimensional structure of these
proteins
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hydrophilic channels selectively permit one type of ion to pass through the membrane
the ion channels that are found in neurons contain …
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… either sodium, potassium, calcium, or chloride ions (Na+, K+, Ca2+, and Cl−) (figure 2.8)
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permeability: extent to which a particular ion can cross the membrane through a given ion channel
membrane permeability to K+ is larger
neurons can change the permeability of their membranes
gated ion channels: ion channels that are capable of changing their permeability for a particular ion
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open or close based on changes in nearby transmembrane voltage
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open or close as a response to chemical or physical stimuli
non-gated ion channels: are unregulated, and hence always allow the associated ion to pass through
Ion pumps
use energy to actively transport ions across the membrane against their concentration gradients
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from regions of low concentration to regions of higher concentration
there are con- centration gradients of different ions across the neuronal
membrane
Na+ and Cl− concentrations are greater outside of the cell
- K+ concentrations are greater inside the cell
- neurons use a Na+/K+ pump that pumps Na+
ions out of the cell and K+ ions into the cell
- this process requires energy
- Each pump is an enzyme that hydrolyzes
adenosine triphosphate (ATP)
- For each molecule of ATP that is hydrolyzed,
the resulting energy is used to move three Na+
ions out of the cell and two K+ ions into the cell
(figure 2.8 and 2.9)
- concentration gradients create forces of the
unequal distribution of ions
- force of the Na + concentration gradient wants to push Na + from an area of high
concentration to one of low concentration (outside to inside)
- K+ con- centration gradient acts to push K+ from an area of high concentration to
an area of low concentration (inside to outside)
- inside and outside voltages are different because the membrane is more
permeable to K+ than to Na +
- electrical gradient: force of the K+ concentration gradient pushes some K+ out of
the cell, leaving the inside of the neuron slightly more negative than the outside
o
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each K+ ion carries one unit of positive charge out of the neuron as it moves across the membrane
These two gradients (electrical and ionic con- centration) are in opposition to one another with respect
to K+ (figure 2.10)
The Action Potential
electrotonic conduction
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Passive current conduction
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maximum distance a passive current will flow is only about
1 millimeter
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diminishes with distance from its origin—the synapse, in
this case
action potential
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a rapid depolarization and repolarization of a small region of
the membrane caused by the opening and closing of ion
channels
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doesn’t decrement after only 1 millimeter
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can travel for meters with no loss in signal strength,
because they continuously regenerate the signal
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giraffes and blue-whales
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metabolically expensive, and it contributes to the inordinate amount of the body’s energy used by the
brain
voltage-gated ion channels
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action potential is able to regenerate itself due to the presence
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located in the neuronal membrane
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are found at the spike-triggering zone in the axon hillock and along the axon
spike-triggering zone
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initiates the action potential
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passive electrical currents that are generated sum together at the axon hillock
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flows across the neuronal membrane in the spike-triggering zone, depolarizing the membrane
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depolarization is strong enough (-70mV to -55mV) – then an action potential is triggered
equilibrium potential
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particular voltage at which there is no net flux of ions
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result = the membrane is temporarily hyperpolarized, meaning that the membrane potential is even
farther from the threshold required for triggering an action potential
hyperpolarization
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causes the K+ channels to close
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resulting in the membrane potential gradually returning to its resting state
during this state -> voltage-gated Na+ channels are unable to open, and another action potential cannot
be generated
refractory period
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lasts only a couple of milliseconds and has two consequences
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the neuron’s speed for generating action potentials is limited to about 200 action potentials
per second
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the passive current that flows from the action potential can- not reopen the ion-gated
channels that generated it
saltatory conduction
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appearance that the action potential is jumping down the axon at great speed, from one node of Ranvier
to the next
Key Points Neuronal Signaling:
- The presynaptic cell is located before the synapse with respect to information flow; the postsynaptic cell is located after the synapse with respect to
information flow. Nearly all neurons are both pre- and postsynaptic, since they both receive and transmit information.
- The resting membrane potential is the difference in the voltage across the neuronal membrane during rest (i.e., not during any phase of the action
potential).
- The electrical gradient results from the asymmetrical distribution of ions across the membrane. The electrical difference across the membrane is the basis
of the resting potential.
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Ion channels are formed by transmembrane proteins that create passageways through which ions can flow.
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Action potentials are an all-or-none phenomenon: The amplitude of the action potential does not depend on the size of the triggering depolarization, as
long as that depolarization reaches threshold for initiating the action potential.
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Ion channels can be either passive (always open) or gated (open only in the presence of electrical, chemical, or physical stimuli).
Passive current conduction is called electrotonic conduction or decremental conduction. A depolarizing current makes the inside of the cell more positive
and therefore more likely to generate an action potential; a hyperpolarizing current makes the inside of the cell less positive and therefore less likely to
generate an action potential.
Voltage-gated channels are of prime importance in generating an action potential because they open and close according to the membrane potential.
Myelin allows for the rapid transmission of action potentials down an axon.
Nodes of Ranvier are the spaces between sheaths of myelin where voltage-gated Na + and K+ channels are located and action potentials occur.
Synaptic transmission
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the transfer of a signal from the axon terminal to the next cell
two major kinds of synapses— chemical and electrical—each
using very different mechanisms for synaptic transmission
Chemical Transmitters
neurons send a signal to the cell across the synapse by
releasing neurotransmitters into the synaptic cleft
arrival of the action potential at the axon terminal leads to the
depolarization of the terminal membrane
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causing voltage-gated Ca2+ channels to open
then triggers small vesicles containing
neurotransmitter to fuse with the
membrane at the synapse and release
the transmitter into the synaptic cleft
(1) transmitter diffuses across the cleft
(2) binds with specific receptors embedded in the postsynaptic
membrane (figure 2.12)
(3) neurotransmitter binding induces a change in the receptor
(4) opens specific ion channels and results in an influx of ions
leading to either depolarization (excitation) or
hyperpolarization (inhibition) of the postsynaptic cell
(5) hyperpolarization of the postsynaptic neuron produces an
inhibitory postsynaptic potential (IPSP)
Synaptic Vesicles – stores various neurotransmitters that are
release at the synapse. The release is regulated by a voltagedependent calcium channel
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Vesicles – essential for propagating nerve impulses
between neurons and are constantly recreated by
the cell
Synaptic Cleft – the gap between neurons and synapses
Receptor – in the cell’s (neuron’s) membrane, receiving
chemical input such as from neurotransmitters
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Ionotropic – ion-channel receptors that accept the
flow of neurotransmitters
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Metabotropic – indirectly allow the flow of
neurotransmitters
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Neurotransmitters (amino acids, biogenic amines, neuropeptides)
Small-molecule: single amino acids
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Acetylcholine (muscle - the chemical that motor
neurons of the nervous system release to activate
muscles
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Monoamines – involved in the regulation of cognitive
processes such as emotion, arousal and certain types
of memory
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Dopamine (pleasure and addiction) – the reward
chemical. The release of dopamine “teaches” the
brain that an activity or stimulus is beneficial.
Overstimulation via dopamine can lead to addiction.
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Serotonin (sleep, eating, depression) – mediates gut
movements and the perceptions of resource
availability
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Amino acid – a simple organic compound
containing both a carboxyl (COOH) and an
amino (NH2) group
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Glutamate – primarily used in learning and
memory. The most abundant
neurotransmitter in the Nervous System,
accounting for 90% of all synaptic
transmissions
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Main brain excitatory –
glutamate stimulates the brain
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GABA – accounts for 90% of all inhibitions
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Main brain inhibitory – GABA,
Serotonin, and other inhibitory
neurotransmitters do not
stimulate the brain. Provides
balance to the excitatory
neurotransmitters
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Neuropeptides – large neurotransmitters, made up of strings of amino acids. Divided into 5 groups
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Tachykinins – pain
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Neurohypophyseal hormones – love, production of urine
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Hypothalamic releasing hormones – stress, growth inhibition
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Opioid peptides – endorphins, feel-good chemicals
Gaseous – believed to be used to stimulate the production of other “messenger chemicals”
Electrical Transmitters
Neuronal membranes are touching at
specializations called gap junctions
The cytoplasms of the two neurons are
essentially continuous
These gap junction channels create pores
connecting the cytoplasm of the two neurons
(figure 2.14)
Result = electrical changes in one are reflected
instantaneously in the other
Useful when information must be conducted
rapidly, such as in the escape reflex of some
invertebrates
Groups of neurons with these synapses can
activate muscles quickly
Key Points Synaptic Transmission:
- Synapses 10^15/per neuron are the locations where one neuron can transfer information to another neuron or specialized non-neuronal cell. They are
found on dendrites and at axon terminals but can also be found on the neuronal cell body.
- Chemical transmission results in the release of neurotransmitters from the presynaptic neuron and the binding of those neurotransmitters on the
postsynaptic neuron, which in turn causes excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs), depending on the properties of the
postsynaptic receptor.
- Classes of neurotransmitters include amino acids, biogenic amines, and neuropeptides.
- Neurotransmitters must be removed from the receptor after binding. This removal can be accomplished by (a) active reuptake back into the presynaptic
terminal, (b) enzymatic breakdown of the transmitter in the synaptic cleft, or (c) diffusion of the neurotransmitter away from the region of the synapse.
- Electrical synapses are different than chemical synapses as they operate by passing current directly from one neuron (presynaptic) to another neuron
(postsynaptic) via specialized channels in gap junctions that connect the cytoplasm of one cell directly to the other.
Overview of the Nervous System Structure
Nervous System Structure
- composed of the central nervous system (CNS), brain and spinal cord, and the
peripheral nervous system (PNS), nerves (bundles of axons and glia) and ganglia
(clumps of nerve cell bodies) outside of the CNS
Peripheral nervous system (PNS):
- courier network delivers sensory information to CNS and carries motor commands
from CNS to muscles
- Consisting of the nerves (bundles of axons and glia) and ganglia (clumps of nerve
cell bodies) outside of the CNS
- Activities of PNS are accomplished
through 2 systems:
- somatic motor system
- controls voluntary muscles
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- autonomic motor system
- controls visceral functions
- involved in controlling the
involuntary action of smooth
muscles (the heart and various
glands)
Autonomic nervous system has 2 subdivisions: sympathetic and
parasympathetic branches (operate antagonistically e.g. sympathetic increases
heart rate, parasympathetic slows it)
sympathetic system
o uses the neurotransmitter norepinephrine
§
activation of this system increases heart rate,
diverts blood from the digestive tract to the
somatic musculature and prepares the body for
action
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flight
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fight
parasympathetic system
o uses acetylcholine as its transmitter
o activation of this system slows heart rate, stimulates digestion and in general helps the body with functions
germane to maintaining the body
Central nervous system (CNS)
made up of the delicate brain and spinal cord
o Each encased in its protective, bony shell and suspended in a sea of cerebrospinal fluid (CSF)
both the brain and the spinal cord are covered with three protective membranes – meninges
outer membrane is the thick mater, the middle is the arachnoid mater and the inner and most delicate is the pia mater
which firmly adheres to the surface of the brain
in the CNS neurons are bunched together in various ways
o Two of the most common organizational clusters are in a nucleus or in a layer
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a nucleus is a relatively compact arrangement of nerve cell bodies and their connections, ranging
from hundred to millions of neurons with similar inputs and outputs
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Located throughout both the brain and the spinal cord
o The outer layer of the brain – cerebral cortex
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has billions of neurons
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arranged in layers if thin sheets, folded across the surfaces of the cerebral hemisphere like a
handkerchief
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cortex has a thin grayish layer overlaying the whitish interior
o The gray matter
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Is composed of neuronal cell bodies
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consisting of neuronal bodies
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resembles a butterfly with two se
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ventral horn contains the large motor neurons that project to muscles
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dorsal horn contains sensory neurons and interneurons
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interneurons project to motor neurons on the same (ipsilateral) and opposite (contralateral) sides
of the spinal cord to aid in the coordination of limb movements
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surrounds the central canal, which is an anatomical ex- tension of the ventricles in the brain and
contains cerebrospinal fluid
o The white matter
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Consist of axons and glial cells
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peripheral region is made up of white matter tracts
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tracts of ascending sensory information and descending motor signals
Key Points Overview of the Nervous System Structure:
The central nervous system consists of the brain and spinal
cord. The peripheral nervous system consists of all nerves
and neurons outside of the central nervous system.
The autonomic nervous system is involved in controlling
the action of smooth muscles, the heart, and various
glands.
It includes the sympathetic and parasympathetic systems.
The sympathetic system uses the neurotransmitter
norepinephrine. This system increases heart rate, diverts
blood from the digestive tract to the somatic musculature,
and prepares the body for fight-or-flight responses by
stimulating the adrenal glands.
The parasympathetic system uses acetylcholine as a
neurotransmitter. It is responsible for decreasing heart
rate and stimulating digestion.
Groups of neurons are called ganglia.
The cerebral cortex is a continuous sheet of layered
neurons in each hemisphere.
The axons of cortical neurons and subcortical ganglia
travel together in white matter tracts that interconnect
neurons in different parts of the brain and spinal cord.
The corpus callosum is the main fiber tract that connects
the two hemispheres of the brain.
The Spinal Cord (figure 2.19)
- Takes in sensory information from the body’s peripheral sensory receptors,
relays it to the brain, and conducts the final motor signals from the brain to the
muscles
- Each level of the spinal cord has a reflex pathway, such as the knee-jerk reflex
mentioned earlier
- Runs from the brainstem at about the first spinal vertebrae to its termination
in the cauda equina (“horse tail”)
- The cauda equina is enclosed in the bony vertebral column – a stack of
separate bones (vertebrae) that extend from the base of the skull to the fused
vertebrae at the coccyx (tailbone)
- vertebral column is divided into sections: cervical, thoracic, lumbar, sacral,
and coccygeal
- spinal cord is similarly divided (excluding the coccygeal region, since we no
longer have tails) into 31 segments
- each segment has a right and a left spinal nerve that enters and exits
from the vertebral column through openings called foramen
- each spinal nerve has both sensory and motor axons: one afferent
neuron carries sensory input through the dorsal root into the spinal
cord, and the other efferent neuron carries motor output through the
ventral root away from it
A Guided Tour of the Brain
when we see a brain, the cerebral cortex, the outer layer, is most prominent
for the brain, the cerebral cortex is the frosting on the cake—it’s the last thing to develop from an evolutionary
at the base of the brain, are structures that are found in most vertebrates and have evolved for hundreds of millions of
years
these parts of the brain control our most basic survival functions, such as breathing, heart rate, and temperature
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the prefrontal cortex, which is found only in mammals, is
evolutionarily the youngest part of our brain
damage to the prefrontal cortex may not be immediately fatal, but
it will likely affect such things as our ability to make decisions as
well as other behaviors that we consider to be most advanced in
humans
the head is merely an appendage to the body, so the terms that
are used to describe the orientation of the head and its brain are in
relation to the body
let’s first picture the body of an Australian shepherd, looking off to
the left
o the front end is the rostral end, meaning “nose.”
o the opposite end is the caudal end, the “tail.”
o along his back is the dorsal surface, just like the dorsal
fin is on the back of a shark.
o the bottom surface along the dog’s belly is the ventral
surface.
o we can refer to the dog’s nervous system by using the
same coordinates
o the part of the brain toward the front is the rostral end
(toward the frontal lobes)
o the posterior end is the caudal end (toward the
occipital lobe)
o along the top of his head is the dorsal surface, and the
bottom surface of the brain is the ventral surface.
we humans are atypical animals because we stand upright and,
therefore, tilt our heads forward in order to be parallel with the
ground
- thus, the dorsal surface of the body and brain
are now at right angles to each other
- in humans, we also use the terms superior and
inferior to refer to the top and bottom of the
brain, respectively
- when we consider the spinal cord, the
coordinate systems align with the body axis
- thus, in the spinal cord, rostral means “toward
the brain,” just as it does in the dog
- if we slice the brain from nose to tail, that is a
sagittal section
- when that slice is directly through the middle, it
is a midsagittal or medial section
- If it is off to the side, it is a lateral section
- If sliced from top to bottom, separating the
front of the brain from the back, we have made a
coronal section
If we slice in a plane that separates dorsal from ventral, that is known as
either an axial, transverse, or horizontal section
The chambers of the Mind
neurons in the brain are functional units, and that how they are interconnected yields specific circuits for the support of
particular behaviors
early anatomists, believing that the head contained the seat of behavior, examined the brain to see where the conscious
self (soul, if you wish) was located
Some chambers in the brain seemed to be empty (except for some fluid) and thus were possible containers for higher
functions - ventricles
brain weighs a considerable amount but has
little or no structural support; there is no
skeletal system for the brain
to overcome this potential difficulty, the brain is
immersed in a fluid called cerebrospinal fluid
(CSF)
this fluid allows the brain to float to help offset
the pressure that would be present if the brain
were merely sitting on the base of the skull
o also reduces shock to the brain and
spinal cord during rapid accelerations
or decelerations, such as when we
fall or are struck on the head
ventricles inside the brain are continuous with
the CSF surrounding the brain
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largest of these chambers are the lateral ventricles, which are connected to the third ventricle in the brain’s midline
cerebral aqueduct joins the third to the fourth ventricle in the brainstem below the cerebellum
CSF is produced in the lateral ventricles and in the third ventricle by the choroid plexus, an out- pouching of blood vessels
from the ventricular wall (hence CFS is similar to blood)
CSF is a clear fluid containing proteins, glucose, and ions, especially potassium, sodium, and chloride
o slowly circulates from the lateral and third ventricles through the cerebral aqueduct to the fourth ventricle and
on to the subarachnoid space surrounding the brain, to be reabsorbed by the arachnoid villi in the sagittal
sinus (the large venous system located between the two hemispheres on the dorsal surface; not shown)
The Brainstem: Medulla, Pons, Cerebellum and Midbrain
three main parts: the medulla (myelencephalon),
the pons and cerebellum (metencephalon), and
the midbrain (mesencephalon)
these three sections form the central nervous
system between the spinal cord and the
diencephalon
though the brainstem is rather small compared
to the vast bulk of the forebrain, it plays a
starring role in the brain
- brainstem
contains groups of
(1)motor nuclei,
(2)sensory nuclei,
(3)nuclei of widespread modulatory neurotransmitter systems, (4)white matter tracts of
ascending sensory information, (5)descending motor signals
- damage to the brainstem = life threatening - brainstem nuclei control respiration and global
states of consciousness such as sleep and wakefulness
- medulla, pons, and cerebellum make up the hindbrain
Midbrain
Brainstem
Hindbrain
Mesencephalon
Metencephalon
Myelencephalon
Cerebellum
Pons
Medulla
Medulla
- brainstem’s most caudal portion is the medulla
- continuous with the spinal cord (figure 2.21)
- essential for life
- houses the cell bodies of many of the 12 cranial nerves, providing sensory and motor
innervations to the face, neck, abdomen, and throat (including taste) as well as the motor nuclei
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that innervate the heart
controls vital functions such as respiration, heart rate, and arousal
all of the ascending somatosensory information entering from the spinal cord passes through the medulla via two bilateral
nuclear groups
gracile nuclei
cuneate nuclei
these projection systems continue through the brainstem to synapse in the thalamus
en route to the somatosensory cortex
the medulla is a relay station for sensory and motor information between the body
and brain
it is the crossroads for most of the body’s motor fibers
it controls several autonomic functions, including the essential reflexes that
determine respiration, heart rate, blood pressure, and digestive and vomiting
responses
Pons
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pons is the main connection between the brain and the cerebellum
Sitting anterior to the medulla
made up of a vast system of fiber tracts interspersed with nuclei
Many of the cranial nerves synapse in the pons (include the sensory and motor nuclei
from the face and mouth and the visuomotor nuclei controlling some of the
extraocular muscles)
important for some eye movements as well as those of the face and mouth
responsible for generating rapid eye movement (REM) sleep
Cerebellum
- The cerebellum clings to the brainstem at the level of the pons
- it is home to most of the brain’s neurons
- it is a continuous layer of tightly folded neural tissue (like an accordion)
- forms the roof of the fourth ventricle and sits on the cerebellar peduncles, which are massive
input and output fiber tracts of the cerebellum
- several gross subdivisions (1)cerebellar cortex (2)four pairs of deep nuclei, (3)the internal
white matter
- resembles the forebrain’s cerebral hemispheres
- inputs from vestibular projections involved in balance, as well as auditory and visual inputs,
also project to the cerebellum from the brainstem
- output from the cerebellum originates in the deep nuclei
ascending outputs travel to the thalamus and then to the motor and
premotor cortex.
other outputs project to nuclei of the brainstem, where they impinge on
descending projections to the spinal cord
- critical for maintaining posture, walking, and performing coordinated movements
- not directly control movements; instead, it integrates in- formation about the body, such as its
size and speed, with motor commands
- then modifies motor outflow to effect smooth, coordinated movements
- if cerebellum = damaged - your movements will be uncoordinated and halting, and you may
not be able to maintain balance
Midbrain (Diencephalon and Telencephalon)
lies superior to the pons and can be seen only in a medial view
surrounds the cerebral aqueduct, which connects the third and fourth ventricles
dorsal portion consists of the tectum
ventral portion is the tegmentum (covering)
contains some of the cranial nerve ganglia and two other important structures
superior colliculi
plays a role in perceiving objects in periphery (the outer limits or
edge of an area or object)
orienting our gaze directly toward them and bringing them into
sharper view
inferior colliculi
used for locating and orienting toward auditory stimuli
red nucleus
involved in certain aspects of motor co- ordination
helps a baby crawl or coordinates the swing of your arms as you walk
Key Points the Brainstem: Medulla, Pons, Cerebellum and Midbrain:
The spinal cord conducts the final motor signals to the muscles,
and it relays sensory information from the body’s peripheral
receptors to the brain.
The brainstem’s neurons carry out many sensory and motor
processes, including visuomotor, auditory, and vestibular
functions as well as sensation and motor control of the face,
mouth, throat, respiratory system, and heart.
The brainstem houses fibers that pass from the cortex to the
spinal cord and cerebellum, and sensory fibers that run from
spinal levels to the thalamus and then to the cortex.
Many neurochemical systems have nuclei in the brainstem that
project widely to the cerebral cortex, limbic system, thalamus,
and hypothalamus.
The cerebellum integrates information about the body and
motor commands and modifies motor outflow to effect smooth,
coordinated movements.
-
The Diencephalon: Thalamus and
Hypothalamus
- After leaving the brainstem, we arrive at the diencephalon, which is
made up of the thalamus and hypothalamus
- These subcortical structures are composed of groups of nuclei with
interconnections to widespread brain areas
Thalamus
- Almost in the center of the brain and perched on top of the brainstem
at the rostral end
- The larger of the two diencephalon structures
- Divided into two parts
Right hemisphere
Left hemisphere
Both straddle the third ventricle
The two parts are connected by a bridge of gray mater called
the massa intermedia (figure 2.23)
- referred to as the “gateway to the cortex” because all of the sensory
modalities make synaptic relays in the thalamus before continuing to the primary cortical sensory receiving areas
receives inputs from the basal ganglia, cerebellum, neocortex, and medial temporal lobe
sends projections back to these structures to create circuits involved in many different functions
thalamus is divided into several nuclei that act as specific relays for incoming sensory information
lateral geniculate nucleus
receives information from the ganglion cells of the retina and sends axons to the primary visual cortex
medial geniculate nucleus
receives information
from the inner ear,
via other brainstem
nuclei in the
ascending auditory
pathway, and sends
axons to the primary
auditory cortex
ventral posterior (medial and
lateral) nuclei
projects
somatosensory
information to the
primary
somatosensory
cortex
pulvinar nucleus
Located at the posterior pole of the thalamus
involved in attention and in integrative functions involving
multiple cortical areas
-
-
Hypothalamus
main link between the nervous system and the endocrine system
main site for hormone production and control
two bumps seen on the ventral surface of the brain (mammillary bodies)
belong to the small collection of nuclei and fiber tracks
receives inputs from the limbic system structures and other
brain areas
job - control circadian rhythms (light–dark cycles) with inputs
from the mesencephalic reticular formation, amygdala, and the
retina
controls the functions necessary for maintaining the normal state of the
body (homeostasis)
sends out signals that drive behavior to alleviate such feelings as (1)thirst,
(2)hunger,(3) fatigue, and it controls body temperature and circadian
cycles
Key Points the Diencephalon: Thalamus and Hypothalamus:
The thalamus is the relay station for almost all sensory information.
The hypothalamus is important for the autonomic nervous system and
endocrine system. It controls functions necessary for the maintenance
of homeostasis. It is also involved in control of the pituitary gland.
The pituitary gland releases hormones into the bloodstream where
they can circulate to influence other tissues and organs (e.g., gonads).
The Telencephalon: Limbic System and Basal Ganglia
includes the cerebral cortex, the limbic system, and the basal ganglia
forms a clump of structures found deep within the cerebral hemispheres nestled over and around the diencephalon
Limbic System
made up of the cingulate gyrus, the hypothalamus, anterior thalamic nuclei, and the hippocampus
cingulate gyrus = a band of cerebral cortex that extends above the corpus callosum in the anterior–posterior
direction and spans both the frontal and
parietal lobes
hippocampus = an area located on the
ventromedial aspect of the temporal lobe
neither anatomically nor functionally organized to
the degree that other systems are in the brain
includes the amygdala, the orbitofrontal cortex and
parts of the basal ganglia
group of neurons anterior to the
hippocampus
Basal Ganglia
collection of nuclei bilaterally located deep in the
brain beneath the anterior portion of the lateral
ventricles
voluntary motor responses, decision making
its components are amygdala, striatum
receive inputs from sensory and motor areas
-
striatum receives extensive feedback
projections from the thalamus
the basal ganglia have many dopamine
receptors
plays a crucial role in motivation and
learning
big role in reward-based learning and goaloriented behavior
Key Points the Telencephalon: Limbic System
and Basal Ganglia:
The limbic system includes
subcortical and cortical structures
that are interconnected and play a
role in emotion.
The basal ganglia are involved in a
variety of crucial brain functions,
including action selection, action
gating, reward-based learning,
motor preparation, timing, task
switching, and more.
Cerebral Cortex
crowning glory of the cerebrum is its
outermost tissue, the cerebral cortex
-
made up of large sheets of (mostly) layered
neurons
draped and folded over the two symmetrical hemispheres
sits over the top of the core structures
including parts of the limbic system and basal ganglia, and surrounds the structures of the diencephalon
infoldings of the cortical sheet are called sulci and gyri (figure 2.28)
- folds of the human cortex serve several functions
they enable more cortical surface to
be packed into the skull
total surface area of the human
cerebral cortex is about 2,200 to 2,400
cm2
-
-
-
-
-
cortex contains the cell bodies of neurons, their dendrites, and
some of their axons
cortex includes axons and axon terminals of neurons projecting
to the cortex from other brain regions, such as the subcortical
thalamus
also contains blood vessels
because of the high density of cell bodies, it appears grayish
(figure 2.29)
Gyri
the crowns of the folded tissue that one observes when viewing
the surface
Dentate Gyrus – simple cortical regions that is an integral
portion of the larger functional brain system called the
hippocampal formation
having a highly folded cortex brings
neurons into closer three- dimensional
relationships to one another
reducing axonal distance and hence
neuronal conduction time between
different areas
the cortex brings some nearby regions
closer together
cortex ranges from 1.5 to 4.5 mm in
thickness, but in most regions, it is
approximately 3 mm thick
Inferior temporal gyrus – placed below the middle temporal sulcus, connected behind with the inferior occipital gyrus, one of
the higher levels of the visual processing associated with the representation of complex object features
Middle temporal gyrus – located between superior temporal gyrus and inferior temporal gyrus, recognition of known faces
Inferior frontal gyrus – speech production
Sulci
furrow of a convoluted brain surface
Central Sulcus – divides frontal from parietal lobes
Lateral sulcus (Sylvian fissure) - separates the temporal lobe from the frontal and parietal lobes
Cortical Layers
are sheets of neurons neatly stacked on top of each other
neurons of each layer are typically similar within a layer, but different
between layers
Molecular layer - contains the flattened dendritic trees of Purkinje cells, and
the huge array of parallel fibers, from the granular layer, that penetrate the
Purkinje cell dendritic trees at right angles
External granular - thin layer consisting of numerous small, densely packed
neurons
External pyramidal - most superficial layer of cerebral cortex
Internal granular - this layer receives the afferent connections from the
thalamus and from other cortical regions and sends connections to the
other layers
Internal pyramidal - consists predominantly of the medium- sized and large pyramidal cells. It is the source of the output or
corticofugal fibers
Multiform (fusiform) layers - the deepest layer of the cortex that directly overlies the subcortical white matter.
Brodmann’s areas (figure 2.31)
- identified approximately 52 regions of the cerebral cortex
- categorized and numbered according to differences in
cellular morphology and organization
- the numbering has more to do with the order in which
Brodmann sampled a region than with any meaningful relation
between areas
- region of the cerebral cortex in the human or other primate
brain, defined by its cytoarchitecture, or histological structure
and organization of cells
Lobes and Basic Functions
cerebral hemispheres have four main divisions (lobes) that are best seen in a lateral view: the frontal, parietal, temporal, and
occipital lobes (figure 2.30)
skull bones them- selves are named for their locations
lobes can usually be distinguished from one another by prominent anatomical landmarks such as pronounced sulci
central sulcus divides the frontal lobe from the parietal lobe
-
Sylvian (lateral) fissure separates the temporal lobe from the frontal and
parietal lobes
occipital lobe is demarcated from the parietal and temporal lobes by the
parieto-occipital sulcus
left and right cerebral hemispheres are separated by the interhemispheric
fissure (figure 2.28b)
insula is located between the temporal and frontal lobe
an island of folded cortex hidden deep in the lateral sulcus
divided into the larger anterior insula and smaller posterior
insula
Occipital lobe (figure 2.35)
- The job of the occipital lobes is vision
- receives visual information relayed from the lateral geniculate nucleus of the thalamus
- In humans, the primary visual cortex is on the medial sur- face of the cerebral hemispheres, extending
only slightly onto the posterior hemispheric pole
- The cortex in this area has six layers and begins the cortical coding of visual features like luminance,
spatial frequency, orientation, and motion
- Visual information from the outside world is processed by
multiple layers of cells in the retina
transmitted via the optic nerve to the lateral geniculate nucleus of the thalamus
from there to V1—a path- way often referred to as the retinogeniculostriate (primary visual
pathway)
Parietal lobe (figure 2.34)
-
- receives sensory information from the out- side world,
sensory information from within the body, and information from memory,
and integrates it
result in all sorts of odd deficits relating to sensation and spatial location
Stimulating certain regions of the parietal lobe causes
people to have “out of body” experiences
Sensory information about touch, pain, temperature sense, and limb
proprioception (limb position) is received via receptor cells on the skin
converted to neuronal impulses that are conducted to the spinal cord
after that conducted to the somatosensory relays of the thalamus (figure
2.34)
Frontal lobe (figure 2.33)
- plays a major role in the planning and execution of
movements
- two main subdivisions: the prefrontal cortex and the motor
cortex
- motor cortex sits in front of the central sulcus, beginning in
the depths of the sulcus and extending anteriorly
- auditory cortex lies in the superior part of the temporal lobe
in a region
- has a tonotopic organization, meaning that the physical layout of the neurons is based on the frequency of sound
Temporal lobe
audition, speech, perception, memory, emotions
(auditory, visual, and multi- modal processing areas)
temporal lobe lies underneath the temporal bone
passage of time can be observed first in the graying of hair
Key Points Cerebral Cortex & Lobes and Basic Function
- Gyri are the protruding areas seen on the surface of
the cortex; sulci, or fissures, are the enfolded
regions of cortex.
- Brodmann divided the brain into distinct regions
based on the underlying cytoarchitectonic.
- The lobes of the brain include the frontal, parietal,
temporal, and occipital lobes.
- The frontal lobe is for planning, cognitive control,
and execution of movements. The parietal lobe
receives sensory input about touch, pain,
temperature, and limb position, and it is involved in
coding space and coordinating actions.
- The temporal lobe contains auditory, visual, and
multi- modal processing areas. The occipital lobe
processes visual information. The limbic lobe (not
really a lobe) is involved in emotional processing,
learning, and memory.
- Topography is the principle that the anatomical
organization of the body is reflected in the cortical
representation of the body, both in the sensory
cortex and motor cortex.
- Association cortices are those regions of cortex outside the sensory specific and motor cortical regions.
Association cortex receives and integrates input
from multiple sensory modalities.
Brain Evolution
Brain Size to body size ratio
Homo Sapiens have the largest brain size to body size ratio
-
Porpoise (and dolphin) are very close
Brain size increase in hominids
During evolution, humans have experienced an exponential
increase in brain size
In a simple life form: every position and function of a nerve cell
is determined by genes
Bigger Brains
A single byte (or 8 bits) can represent 4 DNA base pairs. In order
to represent the entire diploid human genome in terms of bytes,
we can perform the following calculations:
9
9
6×10 base pairs/diploid genome x 1 byte/4 base pairs = 1,5×10 bytes
9
1,5×10 bytes = 1.5 Gigabytes
Number of Neurons
100 billion (10^11)
Arborization of dendrites
At the same time the synaptogenesis is occurring,
neurons of the brain are increasing the size of their
dendritic arborization, extending their axons, and
undergoing myelination
Number of synapses
10 000 per neuron (10^15 synapses)
Radial Unit Hypothesis
Hypothesis
First cells divide symmetrically: they keep the same
function (Symmetrical division)
After this they divide asymmetrically: one cell gets a
different function (ie. Neuron) (Asymmetrical division)
The cortex is formed from an inside-out matter
New neurons migrate radially, you get exponentially more neurons
Radial Unit Hypothesis
First cells divide symmetrically in the ventricular Zone (VZ): keep the same function (Symmetrical division)
After this, they divide asymmetrically: one cell gets a different function (ie. Neuron) and the
differentiated cell migrates to the Cortical Plate (Asymmetrical division)
The cortex is formed from an inside-out manner
From the ventricular zone (VZ) to the cortical plate (CP), deeper layers first
Neuron Migration happens along the radial glial cells
Radial glial cells form radial units from the ventricular zone through the intermediate zone to the cortical
plate
These maintain their topography (relative locations)
Symmetrical division
for the first five to six weeks of gestation, the cells in the subventricular zone divide in a symmetrical
fashion
the result is exponential growth in the number of
precursor cells
Asymmetrical division
At the end of six weeks, when there is a stockpile
of precursor cells, asymmetrical division begins
After every cell division
One of the two cells formed becomes
a migratory cell destined to be part of
another layer
The other cell of the two cells remains
in the subventricular zone
It continues to divide
asymmetrically in the
subventricular zone
Radial glia cells
Stretch from the subventricular zone to the
surface of the developing cortex
Their work does not end with development
Radial glia cells are transformed into astrocytes
in the adult brain
Helping to form part of the
blood-brain barrier
Neurons migrate along the radial glia
cells that form a pathway for the
neurons
Radial migration
Cortical neurons are born and how they
migrate radially from the ventricular
zone toward the surface of the
developing cortex
Neurons migrate along the radial glial
cells
Radial glial highway is organized in a
straight line from the ventricular zone to
the cortical surface
Radial unit Hypothesis
-
The fact that by prolonging the division, we can exponentially increase the number of neurons
Provides the simplest explanation for our enormous increase in brain size
Explains why the cortex is organized in columns
Each unit is not enlarged, instead the number of units increases (**)
Cortical column
A principle unit of organization that has functional consequences and a development history
The cortical columns that arise from (**) these groupings have functional and anatomical consequences
in the adult
Inside-out formation of cortex
In which each cohort of neurons migrates past its cortical plate predecessors to form a more superficial
layer
Ventricular zone
The cortical neurons that form other parts of the brain arise from precursor cells in the ventricular zone
Subventricular Zone
The cortical neurons arise from the subventricular zone
Intermediate Zone
Located between the ventricular zone and the cortical plate
The white matter in this area is where neurons (created in the ventricular zone) migrate through in order
to reach the cortical plate
This zone is only present during carcinogenesis
Eventually transform into adult white matter
Cortical Plate
In humans and many other species, the fetal brain is well developed and shows cortical layers, neuronal
connectivity and myelination
The fetal brain is already extremely complex, but far from completely being developed
The first migrating neurons approach the surface of the developing cortex – point known as cortical plate
Marginal Zone
Predecessor for layer one of the cortex
Marginal zone + cortical zone = 6 layers that form the cortex
Synaptogenesis
Substantial amount of that growth comes from
synaptogenesis
The formation of synapses and the growth of dendritic trees
Early – in the deeper cortical layers
Later – in more superficial layers
Synaptogenesis – followed by synapse elimination (also called
pruning)
Synapse elimination/pruning
Synaptic pruning is a competitive process
Allows for learning development of higher cognitive functions
The elimination of some synaptic contacts between neurons
during development, including postnatally
Eliminating the interconnections between neurons that are redundant, unused or do not remain functional
Myelination
Differential timing in human development
Myelination of axons extends even further into life
Axons in different cortical areas myelinate at different times
Sensory and motor areas first
Frontal and parietal areas last
Myelination of frontal cortex continues way into adulthood :)
Until age 25-30
Use it now (in your 20s) or never get it
Ontogeny = Phylogeny
Ontogeny recapitulates phylogeny
Delayed maturation of the frontal lobes is an example of ontogeny following phylogeny
A late addition in evolution means late development
Brain Plasticity
The brain also displays enormous potential for plasticity after complete development
!!! your brain constantly changes!!!
The brain can recruit other areas that are/were
used for something else (Areas from the
somatosensory cortex that are not used anymore
are recruited by other parts)
Reason why blind people can hear and
feel better
Term that refers to the brains ability to change and
adapt as a result of experience
Learning
Mostly connectivity: synaptic changes
Reorganization
The brain can repair or reorganize after
an accident
Phantom limbs
the ability to feel sensations
and even pain in a limb or
limbs that no longer exist
Non-painful sensation:
perception of movement and
perception of external sensations (touch, temperature, pressure, vibration, itch)
Pain sensations: range from burning and shooting pains to feelings of tingling “pins and
needles”
Only occurs in amputees
Basic Genetics
Chromosomes
My chromosomes make me an individual
Each chromosome consists of genes
Genes
A gene encodes a functional element (protein)
A gene consists of a code (triplets of nuclei acids)
DNA
DNA is deoxyribonucleic Acid
Consist of four bases: cytosine (C), guanine (G), adenine (A), or thymine (T)
Base pairs: C – G and A – T
When we reproduce, our DNA is combined with that of our partner
Genotype
The genes
Phenotype
How they are expressed
Recombination and cross-over
Combine two individuals
Mutation
Randomly alter a bit (usually low)
Genetic Algorithms
Genotype strings and individuals
A genetic algorithm has a large number of
strings/genotypes
Each genotype is also called an individual
Populations
A collection of individuals is called a population
Fitness value/function
Each string/genotype/individual is assigned a fitness
value according to phenotype
This value can be normalized to a range between 0 and 1
You can use anything you like to calculate your fitness value
Reproduction
Cross-over
You have various forms of cross-over
The simples form is single-point cross-over
00110110 x 11001101 = 11000110 x 00111101
It is also possible to have multiple cross-over points
00110110 x 11001101 = 00101110 x 11010101
Inversion
we select a subset of genes and invert the entire string in the subset
0123456789 x 0165432789
Mutation
There are various types of mutation, depending on
your representation
Binary mutation: 001100 = 001110
Selection strategies
Elitist selection
Order individuals by fitness
Select top -10, -20, … fittest individuals
Pro: very straightforward to implement, very fast
Con: each generation loses a lot of genetic information,
“genetic degeneration”
Roulette wheel selection
The wheel is rotated
The weakest individual has smallest share of the roulette
wheel
The fittest individual has largest share of the roulette wheel
Pro: better than elitist selection
Con: comes very close to elitist selection if fitness values are
very unequal
Tournament selection
Select random k individuals (k=tournament size)
From this selection: select the best individual
Pro: Very straightforward; does not have problems of roulette wheel selection
Con: a large k boils to elitist selection
Genetic Algorithms Pros and Cons
Advantages
Widely acceptable
Easy to implement
Easy to parallelize
Disadvantages
Same local minima problem as with back-prop, but
genetic algorithms are better suited to escape local
minima
Lots of variation (e.g. Selection, parameters)
Sometimes difficult to find right encoding
Genetic Algorithms applications
Scheduling problems
Financing
Complex mathematical problems
Engineering: NASA, Intel
Chemistry
Compilers
Exoskeleton
Airforce Strategy Advisor
Airbus
Cognitive Control
Allows us to use our perceptions, knowledge, and goals to bias the selection of action and thoughts
from a multitude of possibilities
Allow us to override automatic thoughts and behavior and step out of the realm of habitual
responses
Give us cognitive flexibility, letting us think and act in novel and creative ways
By being able to suppress some thoughts and activate others, we can simulate plans and consider
the consequences of those plans
We can plan for the future and troubleshoot problems
Essential for purposeful goal- oriented behavior and decision making
„you might want to stop at the doughnut store when heading to work in the morning, cognitive control
mechanisms can override that sugary urge, allowing you to stop by the café for a healthier breakfast “
-
Anatomical Orientation picture:
first, which includes the lateral pre- frontal cortex and frontal pole
supports goal-oriented behavior
involved with planning, simulating consequences, and initiating, inhibiting,
and shifting behavior
second control system, which includes the medial frontal cortex
essential role in guiding and monitoring behavior
works in tandem with the prefrontal cortex
monitoring ongoing activity to modulate the degree of cognitive control
needed to keep behavior in line with goals
Sensation and Perception
Visible light spectrum
segment of electromagnetic spectrum that the human eye
can view
human eye can detect wavelengths from 380 to 700
nanometers
Longer wavelengths (red)
Shorter wavelengths (blue)
Eye
Iris
-
the colored part
-
the black circular opening in the iris
let’s light in
pupil size is adjusted to filter the amount of light
smaller for bright light
larger for low light
Pupil
Cornea
-
-
Lens
-
Retina
-
-
a clear dome over the iris
protective outer layer
serves as barrier against dirt, germs, and other things that
can cause damage
also filters out some of the sun’s ultraviolet light
as light enters your eye, it gets refracted by the corneas
curved edge
helps determine how well you can focus on
objects close-up and far away
Three main layers
Epithelium
Stops outside matter from getting
into your eye
Also absorbs oxygen and nutrients
from tears
Stroma
Middle (thickest) layer lies behind epithelium
Made up mostly of water and protein that give it an elastic but solid form
Endothelium
Single layer of cells on the very back of the stroma
Stroma absorbs excess liquid and the endothelium pulls it out
Without this function the stroma would become waterlogged
Focuses light rays onto the retina
Lens is transparent
Can be replaced if necessary
Lens deteriorates as we age – result – needing
reading glasses
Nerve layer lining the back of the eye
Retina senses light and creates electrical impulses
These impulses are sent through the optic
nerve to the brain
Sees pictures upside down
Optic nerve
Bundle of more than a million nerve fibers carrying visual messages from the retina to the brain
In order to see we must have light and our eyes must be connected to the brain
The brain controls what you see, since it combines images
Retina sees pictures upside down – brain turns images right side up
Reversal of the images that we see – like mirror in a camera
Inverted projection on retina
Images of the world that surrounds us are projected upside down onto our retina
Image reversal – allows us tremendous peripheral vision and ability to see objects larger
Retina
Without reversal – limited view of our world (similar to viewing the world through a drinking straw)
Blind Spot
Small portion of the visual field of each eye
Corresponds to the position of the optic disk within the retina
No photoreceptors (rods or cones) in optic disk
Therefore, no image detection in this area
Blind spot of the right eye is located to the right of the center of vision
Blind spot of the left eye is located to the left of the center of vision
With both eyes open – blind spots not
perceived because the visual fields of the
two eyes overlap
Optic Disk
Can be seen in the back of the
eye with an ophthalmoscope
Located on the nasal side of the
macula lutea
Oval shape
1.5 mm in diameter
Entry point into the eye for
major blood vessels that serve
the retina
Fovea
-
Small, central pit composed of closely packed cones in the eye
Located in the center of the macula lutea of the retina
Responsible for sharp central vision
Necessary in humans for activities for which visual detail – primary importance
Surrounded by parafovea belt and perifovea outer region
Employed for accurate vision in the direction where it is pointed
Compromises less than 1% of the retinal size
Takes up over 50% of the visual cortex
Sees only the central two degrees of the visual field
The farther away from the fovea the fewer receptor
Central region of the retina that is densely packed with cone cells and provides high resolution visual
information
Receptors
Rods
Cones
-
Responsible for vision at low light levels (scotopic
vision)
Usually located around the boundary of the retina
About 120 million photoreceptors out of the total 125
million photoreceptors in the human eye
Outer segment is cylindrical – contain rhodopsin
pigment (made up of vitamin A)
Do not give color vision
Do not have any differentiation
If lack of the pigment in the rods = night blindness
Fewer in number and are of cone shape
Located in the center of the retina
5 million photoreceptors out of 125 million
Outer segment is conical of cones (contain iodopsin
pigment)
Give color vision
If lack of pigment – cause color blindness
Chromatic (three types of pigment):
Short wavelength
-
The blue part of the spectrum
Medium wavelength
The greenish region
Long wavelength
The reddish region
Ganglion cells
Final output neurons of the vertebrate retina
Collect information about the visual world from bipolar
cells and amacrine cells
Process visual information
Begins as light entering the eye
Ganglion cells transmit it to the brain via their
axons
We have only 2 million ganglion cells to telegraph
information from the retina
Many rods feed into a single ganglion cell
Each ganglion cell is innervated by only a few cones
Bipolar cell
Part of the retina
Exist between photoreceptors (rod cells and cone cells) and
ganglion cells
They act directly or indirectly
To transmit signals from the photoreceptors to the ganglion
cells
Receive synaptic input from either rods or cones, or both
Horizontal cell
Laterally interconnecting neurons having cell bodies in the
inner nuclear layer of the retina
Help integrate and regulate the input from multiple
photoreceptor cells
Receive input from multiple photoreceptor cells
use that input to integrate signaling from different populations of photoreceptor cells
Adjust the signals that will be sent to bipolar cells
Amacrine cells
Lie in the inner retina
Make connections with bipolar cells and ganglion cells
Create functional subunits within the receptive fields of many ganglion cells
contribute to vertical communication within retinal layers
Figure 5.23 shows how visual
information is conveyed from the
eyes to the central nervous
system. Before entering the brain,
each optic nerve splits into two
parts. The temporal (lateral)
branch continues to traverse
along the ipsilateral side. The
nasal (medial) branch crosses over
to project to the contralateral
side; this crossover place is called
the optic chiasm.
Lateral inhibition
- The phenomenon in which a neurons response to a stimulus is inhibited by the
excitation of a neighboring neuron
- Observed in the retina and the lateral geniculate nucleus (lgn) of organisms
- Makes neurons more sensitive to spatially varying of stimulus than to spatially
uniform stimulus
- Helps refine some somatosensory information
- Only the neurons that are most stimulated and least inhibited respond
- Plays an important role in visual perception by increasing the contrast and resolution of visual stimuli
Contrast enhancement
Defined as the manipulation and redistributing the image
pixels in a linear or non-linear fashion
Improve the separation of obscured structural
variations in pixel intensity into a more visually
differentiable structural distribution
Required to increase the quality of low contrast images by
expanding the dynamic range of input gray level contrast
enhancement without disturbing other parameters of the
image is one of the difficult tasks in image processing
Visual system
Comprises the sensory organ (eye) and parts of the central nervous system (the retina containing photoreceptor
cells, the optic nerve, the optic tract and the visual cortex)
Gives organisms the sense of sight
Enabling the formation of several non-image photo response functions
-
Detects and interprets information from the optical spectrum perceptible to that species to “build a
representation” of the surrounding environment
Carries out number of complex tasks
Reception of light and the formation of monocular neural representation
Color vision
The neural mechanisms underlying stereopsis and assessment of distances and between
objects
Identification of particular object of interest
Motion perception
Analysis and integration of visual information
Pattern recognition
Accurate motor coordination under visual guidance
Eye
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Light entering the eye is refracted
As it passes through the cornea
Then passes through the pupil (controlled by the iris)
Further refracted by the lens
Cornea and lens act together as a compound lens
To project an inverted image onto the retina
Optic chiasm
Optic nerves from both eyes meet and cross at the optic chiasm
At the base of the hypothalamus of the brain
The information coming from both eyes is combined
Then splits according it the visual field
Corresponding halves of the field of view (left & right)
Sent to the left and right halves of the brain to be processed
The right side of primary visual cortex deals with the left half of the field of view from both eyes (similarly
for the left brain)
Small region in the center of the field of view is processed redundantly by both halves of the brain
lgn
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Lateral geniculate nucleus
Sensory relay nucleus in the thalamus of the brain
Consists of six layers in humans and other primates starting from catarhinias (including
apes)
One type of ganglion cell (m cell) sends output to the bottom two layers
Another type of ganglion cell (p cell) projects to the top four layers
Visual information reaching the cortex has been processed by at least four distinct
neurons
Photoreceptors
Bipolar cells
Ganglion cells
Lgn cells
Lgn cells have receptive fields responding
If the stimulus falls within a very limited region of space (one degree of visual angle)
Layers 1, 4, 6 – correspond to information from the contralateral (crossed) fibers of the nasal retina
(temporal visual field)
Layers 2, 3, 5 – correspond to information from the ipsilateral (uncrossed) fibers of the temporal retina
(nasal visual field)
Visual cortex
Largest system in the human brain
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Responsible for processing the visual image
Lies at the rear of the brain above the cerebellum (highlighted in the photo)
Primary visual cortex (v1) - region that receives information directly from the lgn
V1
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Initial cortical processing area for vision
Located in the most posterior portion of the occipital lobe (brodmann area 17)
Most studied visual area in the brain
In mammals it is located in the posterior pole of the occipital lobe
Simplest, earliest cortical visual area
Highly specialized for processing information about static and moving objects
Excellent in pattern recognition
Equivalent to the striate cortex (brodmann area 17 – defined by its anatomical location)
Cells in v1 have slightly larger receptive fields
This magnification process continues through the visual system
Cells in the temporal lobe have receptive fields that may encompass an
entire hemifield
simple cells
mainly in layers 4 and 6
Have distinct excitatory and inhibitory
regions
Cell that responds primarily to oriented
edges and gratings
Such cells are tuned to different
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frequencies and orientations
Calculate edges
Complex cells
Can be found in the v1, v2, v3
Will respond primarily to oriented edges and gratings
However, it has a degree of spatial invariance
Means – receptive field cannot be mapped into fixed excitatory and
inhibitory zones
Some respond to patterns of light in a certain orientation within a large
receptive field
Regardless of the exact location
Some respond optimally only to movement in a certain direction
In v2
Use the information from many simple cells to represent corners and
edge terminations
End-stopped cells
Are thought to detect singularities like line and edge crossings, vertices and line
endings
Neuron in any visual area of the cerebral cortex
Maximally responsive to a line of a certain length or to a corner of a larger stimulus
Reduced or absent response when the line or corner is extended beyond a certain
point
Orientation columns
Organized regions of neurons
Excited by visual line stimuli of varying angles
Columns are located in the primary visual cortex (v1) and span multiple cortical layers
Neurons with similar properties are arranged in columns perpendicular to the surface of the cortex
Range the six cortical layers until they reach the white matter
Contralateral projection
Between hemisphere and the correspondent side of the body
Example: moving the right hand will make the left hemispheres activity go up
Upside-down projection
'Images' in your brain are just collections of neural activations, and not actual pictures
They cannot have an orientation
brain is capable of flipping your visual field if required as measured through perceptual adaptation
experiments using inversion glasses
Receptive fields
Center-surround receptive field
Allows ganglion cells to transmit information
Whether photoreceptor cells are exposed to light
About the differences in firing rates of cells in the center and surround
This allows the ganglion cells to transmit information about contrast
Size of the receptive field governs the spatial frequency of the information
Small receptive fields
Stimulated by high spatial frequencies (fine detail)
Large receptive fields
Stimulated by low spatial frequencies (coarse detail)
Retinal ganglion cell receptive fields convey information about:
Discontinuities in the distribution of light falling on the retina
Often specify the edges of objects
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Retinotopy / retinal mapping / retinally mapped
Mapping of visual input from the retina to neurons
Particularly those neurons within the visual stream
Retinotopy mapping in humans is done with functional magnetic resonance imaging (fmri)
Subject inside the fmri machine focuses on a point
Then retina – stimulated with a circular image or angled lines about focus point
Radial map displays the distance from the center of vision
Angular map shows angular location using rays angled about the center of vision
Combining both maps – you can see separate regions of the visual cortex
Visual pathways
Eye to V1, V2
Magnocellular
Also called M-cells
Neurons located within the Adina magnocellular layer of the lateral
geniculate nucleus (LGN) of the thalamus
Part of the visual system
Characterized by their relatively large size compared to parvocellular
cells
Receive input from parasol ganglion cells
Cannot provide finely detailed or colored information, but still provides
useful static, depth and motion information
High light/dark contrast detection
More sensitive at low spatial frequencies than high spatial frequencies
Important for providing information about the location of objects
Can detect the orientation and position of objects in space, information that is sent
Information = important – detecting the difference in positions of objects on the
retina of each eye (important tool in binocular depth perception)
Cells in the M pathway – ability to detect high temporal frequencies and can detects quick
changes in the positions of an object
Parvocellular
Also called P-cells
Neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the
thalamus
More modern than M-cells
Receive their input from midget cells (type of ganglion cell) (axons of midget cell are exiting
the optic tract)
Information from each eye is kept separate at this point and continues to be segregated –
until processing in the visual cortex
Sensitive to color and capable of discriminating fine details than the M cell
Greater spatial resolution than M cells
Lower temporal resolution than M cells
Koniocellular
Neuron with a small cell body
Located in the koniocellular layer of the LGN (in primates and humans)
Quantity of neurons = number of M cells
Present between the layers (picture)
Koniocellular layers are much thinner due to their size
Neurochemically and anatomically distinct from M and. P cells
Three proteins
Calbindin
Alpha subunit of type II calmodulin-dependent protein kinase
Gamma subunit of protein kinase C
Some cells respond to color
Some reacts to achromatic gratings
Contribute to brightness contrast information and color contrast in species with color vision
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Contribute to eye movement-related signals
After V2
Dorsal (‘where’ or ‘how’)
Involved in guidance of actions (eg. Reaching) and recognizing where
objects are in space
Also known as parietal stream, where stream, how stream
Stretches from the primary visual cortex (V1) in the occipital lobe
forward into the parietal lobe
Interconnected with the parallel ventral stream (what stream)
Commences with purely visual functions in the occipital lobe
Gradually transferring to spatial awareness
Termination in parietal lobe
Posterior parietal cortex = essential for “the perception and interpretation of spatial relationships,
accurate body image, learning of tasks involving coordination of the body in space”
Contains individually functioning lobules
Lateral intraparietal sulcus (LIP) contains neurons that produce enhanced activation when attention is
moved onto the stimulus
Ventral intraparietal sulcus (VIP) where visual and somatosensory information are integrated
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Perception
Ventral (‘what’)
- Associated with object recognition and form representation
- Described as “what” stream
- Strong connections to
The medial temporal lobe (stores long-term memories)
The limbic system (controls emotions)
Dorsal stream (deals with object locations and motion)
- Gets main input from the parvocellular layer of the LGN of the thalamus
These neurons project to
V1 sublayers 4Cß, 4A, 3B, 2/3a
From there the ventral pathway goes through V2
and V4 to areas of the inferior temporal lobe
Areas of the inferior temporal lobe
- Posterior inferotemporal (PIT)
- Central inferotemporal (CIT)
- Anterior inferotemporal (AIT)
- Each visual area contains a full representation of visual space
It contains neurons whose receptive fields together
represent the entire visual field
Visual information enters the ventral stream through the
primary visual cortex
Travels through the rest of the areas in sequence
All areas in the ventral stream – influenced by extraretinal factors
Attention
Working memory
Salience
Damage to ventral stream – inability to recognize faces or interpret facial expressions
Perception is a unified whole (binding problem)
- Ability of the brain to construct uniform perceptions from a multitude of sensory impressions
- In the visual system, structures are known that are activated more strongly by certain shapes, colors or movements
in their receptive field than when other patterns are shown
- The property of some neurons is the basis of the idea that the sensory information is broken down into such "basic
components"
- and then put back together again – question?
- The binding problem raises the question of how these signals are linked to the overall impression
Pathways for visual perception
Ventral stream
Dorsal stream
Computational problems in perception
Object constancy
Also called perceptual constancy
Tendency of animals and humans to see familiar objects as having standard shape, size, color, or location
Regardless of changes in the angle of perspective, distance or lighting
Impression rends to conform to the object as it is or is assumed to be, rather than to the actual stimulus
Responsible for the ability to identify objects under various conditions
Seem to be “taken into account” during a process of mental reconstitution of the known
image
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Reduced by limited experience with the object and by decreasing the number of environmental cues that
aid in identification of the object
View-invariant recognition
Does not happen by simple analysis of the stimulus information
The perceptual system extracts structural information about the components of an object and the
relationship between these components
key to successful recognition is that critical properties remain independent of
viewpoint
Bicycle example
The properties might be features such as an elongated shape
running along the long axis, combined with a shorter, stick-like
shape coming off of one end
With two circular- shaped parts, we could recognize the object as
a bicycle from just about any position
View-dependent recognition
Posit that people have a cornucopia of specific representations in memory
Key idea is that the stored representation for recognizing a bicycle from the
side is different from the one for recognizing a bicycle viewed from above
Our ability to recognize that two stimuli are depicting the same object is assumed to arise at a later stage
of processing
They seem to place a heavy burden on perceptual memory
Each object requires multiple representations in memory, each associated with a different vantage point
Shape encoding
recognition involve hierarchical representation in which each successive stage
adds complexity
Simple features such as lines can be combined into …
Edges
Corners
Intersections
… which are grouped into parts and the parts grouped into objects
(as processing continues up the hierarchy)
People recognize a pentagon because it contains five-line segments of equal
length (joined together) to form five corners that define an enclosed region
(figure 6.12)
The same five-line segments can define other objects such as a pyramid
Here there are only four points of intersection (not five) and the lines
define a more complicated shape that implies – three dimensional
Investigate how to encode
Identify areas of the brain that are active when comparing contours
that form a recognizable shape versus contours that are just jungled
grand-mother cell coding
Assumption that the final percept of an object is coded by
a single cell
Cells are constantly firing and refractory
Coding scheme of this nature would be highly
susceptible to error
If a gnostic unit were to die, we would expect to
experience a sudden loss for an object
Cannot adequately account for how it is possible to
perceive novel objects
gnostic theory does not account for
how the grandmother cell would have to adapt as
grandmother changed over time
The type of neuron that can recognize a complex
object has been called a gnostic unit (from the Greek
gnostikos, mean- ing “of knowledge”), referring to the
idea that the cell (or cells) signals the presence of a
known stimulus—an object, a place, or an animal that
has been encountered in the past.
Ensemble coding
Recognition is not due to one unit but to the collective
activation of many units
Readily account for why we can recognize similarities
between objects and may confuse one visually similar
object with another
Both objects activate many of the same
neurons
Losing some units might degrade our ability to recognize
an object, but the remaining units might suffice
Account for our ability to recognize novel objects
Novel objects bear a similarity to familiar things
Our percept results from activating units that represent their features
Mind reading
Encoding
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Transform sensory data into a form of mental representation
In storage you keep encoded information in memory
In retrieval you pull out or use information stored in memory
Refers to how you transform a physical, sensory input into a
representation that van be placed into memory
Encode our memories to store them
Short term storage
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Short term memory
Acoustic code is more important than a visual code
Semantics did not matter much for processing
Appears to be primarily acoustic
May be some secondary visual information than acoustic information
Long term storage
Most information stored in long term memory primarily is encoded semantically
Acoustic information, semantic information, visual information – encoded in long term
memory
Decoding
Decoding techniques interrogate more of the
information in the brain scan
Rather than asking which brain regions respond
strongly to faces
They use both strong and war responses to
identify subtler pattern of activity
These recordings are fed into a “pattern classifier”
(computer algorithm that learns the patterns
associated with each picture or concept)
Once a program has seen enough samples it can start
to conclude what the person is looking at or thinking about
Pattern recognition
Cognitive process that matches information from a stimulus with information retrieved from memory
Occurs when information from the environment is received and entered into short-term memory
Causing automatic activation of a specific content of long-term memory
Super important for humans and animals
Koala uses pattern recognition to find and consume eucalyptus leaves
Development of neural networks in the outer layer of the brain in humans has allowed for better
processing of visual and auditory patterns
Six main theories of pattern recognition
Template matching
Mist basic approach to human pattern recognition
Theory – assumes: every perceived object is stored as a “template” into long-term
memory
Incoming information is compared to these templates to find an exact match
Example
A a a are all recognized as a but not b
This theory – can’t explain how new experiences can be understood without being
compared to an internal memory template
Prototype-matching
Compares incoming sensory input to one average prototype
Proposes – exposure to a series of related stimuli leads to the creation of a
“typical” prototype based on their shared feature
Reduces number of stored templates by standardizing them into a single
representation
Supports perceptual flexibility – allows for variability in the recognition of novel
stimuli
Example
Suppose a child has never seen a lawn chair before, but given the
characteristics of a regular chair, the child would still be able to
recognize it as a chair
Feature analysis
Try to explain how humans are able to recognize patterns in their environment
Proposes – nervous system sorts and filters incoming stimuli to allow the human or
animal to make sense of the information
Proposes an increasing complexity in the relationship between detectors and the
perceptual feature
When features repeat or occur in a meaningful sequence
We are able to identify these patterns because of our feature detection
system
Recognition-by-components
Proposes – humans recognize objects by breaking them down into their basic 3d
geometric shapes called geons
Example
Break down something like a coffee cup
We have the hollow cylinder that holds the liquid and a
curved handle off the side that allows to hold it
Bottom-up
Data driven processing
Originates with the stimulation of the sensory receptors
Claims – perception can be explained solely in term of the environment
Stated – sensation is perception and there is no need for extra interpretation as
there is enough information in our environment
Example
Holding a flower at the center of a person’s fields. The sight of the
flower and all the information about the stimulus are carried from the
retina to the visual cortex in the brain
Top-down
Refers to the use of background information in pattern recognition
Always begins with a person’s previous knowledge and makes predictions due to
this already acquired knowledge
We construct our perception of reality and these perceptions are hypotheses or
propositions based on past experiences and stored information
Formation of incorrect propositions will lead to errors of perception – visual
illusions
Example
Given a paragraph written in hard-to-read handwriting
Easier to understand if you read the whole paragraph
(instead of reading the words in separate terms)
Brain may be able to perceive and understand the main idea
of the paragraph
Due to the context supplied by the surrounding
words
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Vicarious ai & deep learning
deep learning
Also known as deep structured learning
Applied to fields including:
Computer vision
Machine vision
Speech recognition
Natural language processing
Audio recognition
Social network filtering
Etc.
“deep” because of the use of multiple layers in the network
Part of a broader family of machine learning methods
Based on artificial neural networks with
representation learning
Learning can be supervised, semi-supervised or unsupervised
Supervised
Machine learning a function that maps an
input to an output based on example input
and output pairs
Semi-supervised
Approach to machine learning that
combines a small amount of unlabeled
data (can produce considerable improvement in learning accuracy) during training
Unsupervised
Type of machine learning that looks for previously undetected patterns in a data set with no
pre-existing labels (minimum human supervision)
memory
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Storage of retrievable information, outcome of learning
Encoding
Processing if new information
Two types of encoding
Acquisition
Sustaining some of the sensory stimuli to
enter into memory
Sensory systems are constantly being
bombarded by tons of stimuli
Most only produce a very brief
transient sensory response hat
fade quickly (1000 ms after
representation)
During this period the stimuli are available for processing
State called a sensory buffer
Only some of these stimuli are sustained and make the cut into short term memory
(acquisition)
Consolidation
Stabilize a memory over time resulting in long term memory
This can occur over days to months even years
Creates a stringer representation over time
Storage
Represents the permanent record of the information
Result of acquisition and consolidation
Retrieval
Accessing stored information
Using it to create a conscious representation or to execute a learned behavior such as a motor act
anatomy of memory
Hippocampus
Embedded deep into the temporal lobe
Major role in learning and memory
Part of the limbic system (which regulated emotions)
Processes long-term memory and emotional responses
If this is being removed
Severe anterograde amnesia of declarative memory
Learn new skills but not remember learning
Essential for memory consolidation
Active when new information is encoded
Also involved in the retrieval if information from long-term
memory
Place cells
Pyramidal neuron within the hippocampus
Becomes active when entering a particular place in its environment
Act as a cognitive representation of a specific location in space known as a cognitive map
Provide evidence that the hippocampus has cells that encode contextual information
Entorhinal cortex
Area of the brain located in the medial temporal lobe
Functions as a hub in a widespread network for memory, navigation and the perception of time
Main interface between the hippocampus and neocortex
Plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial
memories
Memory formation, memory consolidation, and memory optimization in sleep
Also responsible for the pre-processing (familiarity) of the input signals
Association of impulses from the eye and the ear occurs in the entorhinal cortex
Grid cells
Type of neuron within the entorhinal cortex
Fires at regular intervals as an animal navigates an open area
allowing it to understand its position in space by storing and integrating
information about
Location
Distance
Direction
Have been found in animals (rats, mice, bats, monkeys) and humans
Unique properties
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have firing fields over the entire environment (place fields are restricted to certain specific
regions of the environment)
firing fields are organized into hexagonal
Hexagonal lattice
lattice
Firing fields are generally equally spaced apart
such that the distance from one firing field to all six adjacent firing fields is
approximately the same
Firing fields are equally positioned
Such that six neighboring fields are located at approximately 60
degree increments
Standard consolidation theory (squire)
memory consolidated fast in the hippocampus
Via entorhinal cortex
During sleep consolidated in other parts of cortex
Proposed by larry squire and his colleagues
Considers the neocortex to be crucial for the storage of fully consolidated
long-term memories
Considers - the hippocampus plays a temporary role
In this view:
The representation of an event that are distributed throughout
the cortex come together in the medial temporal lobe
The hippocampus binds them
Then through some sort of interaction between the medial temporal lobe and the neocortex,
the bound information – slowly transferred and replaced by a permanent memory trace (in
the neocortex)
Occurs after repeated reactivation of the memory, creates direct connections within the cortex between
the various representations
Process takes place when being asleep or awake
Eventually makes the memory independent of the hippocampus
Key Points Memory and Anatomy of Memory
Learning is the process of acquiring new information, the outcome of which is memory
Learning and memory have many stages including encoding, storage and retrieval
What is known as the medial temporal lobe memory system is made up of the hippocampus and the surrounding rhinal and
parahippocampal cortices
Other areas involved with memory include the prefrontal cortex, the parietal cortex and subcortical structures
The hippocampus is critical for the formation of long- term memory.
Cortex surrounding the hippocampus is critical for normal hippocampal function in memory.
The delayed non-match to sample task is used to assess memory in non-human primates.
The amygdala is not a crucial part of the system for epi- sodic memory, but it is important for emotional memory.
Neurons that activate when rats are in a particular place and facing a particular direction have been identified in the hippocampus and are
called place cells. They provide evidence that the hippocampus has cells that encode contextual information.
types of memory
Long term memory
Declarative (explicit) memory
Defined as memory for events and
for facts, both personal and
general, that we have conscious
access to and that can be verbally reported
Dependent on the medial temporal lobe
Can be broken down into two memories
episodic memory
Memories of personal experience
That we recall about our own lives and what, where, when and with
whom they happened
They differ from personal knowledge
Example (1)
You have personal knowledge of what day you were born
but you do not remember the experience
Always include the self as the agent or recipient of some action
Example (2)
The memory of falling off your new red bi- cycle (what)
on christmas day (when), badly skinning your elbow on
the asphalt driveway (where), and your mother (who)
running over to comfort you is an episodic memory
The result of rapid associative learning in that the what, where,
when, and who of a single episode
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Semantic memory
Is objective knowledge that is factual in nature but does not include the con- text in which it
was learned
Example (1)
You may know that corn is grown in iowa, but you most likely don’t re- member
when or where you learned that fact
Fact can be learned after a single episode, but it may take many exposures
Reflects knowing facts and concepts such as how to tell time, who the lead guitarist is for the
rolling stones, and what quantum mechanics is all about
Nondeclarative (implicit) memory
It cannot be “declared,” that is, verbally reported
Also known as implicit memory
Knowledge that we have no conscious access to
Several types of memory fall under this category: priming, simple learned behaviors that derive from
conditioning, habituation, sensitization, and procedural memory, such as learning a motor or cognitive
skill
This form of memory is revealed when previous experiences facilitate performance on a task that does
not require intentional recollection of the experiences
Is not dependent on the medial temporal lobe
Involves other brain structures, including the basal ganglia, the cerebellum, the amygdala, and the
neocortex
Procedural memory
One form of nondeclarative memory
Depends on extensive and repeated experience
Tasks that require us to use procedural memory include learning motor skills like how to ride a
bike, type, or swim, and learning cognitive skills such as how to read
One test of procedural learning is the serial reaction time task
participants sit at a console
having four buttons
Placing the fingers of one hand
over the buttons, participants
would press buttons that
correspond to locations of
stimuli in front of them
Each button corresponds to
one of four lights
The mapping between button
and light can simply be their spatial relationships
The task would be to press the button with the finger that corresponds to the light
that is illuminated
The lights can be flashed in different sequence
Over time, normal participants respond faster to the repeating sequence than they do to a
totally random sequence
Their improved performance indicates that they have learned the sequence
When asked whether the sequences were random, however, participants report that the
sequences were completely random
Do not seem to know that any pattern existed, yet they learned the skill
Such behavior is typical of procedural learning, which requires no explicit knowledge about
what was learned
Patients with disorders of the basal ganglia or inputs to these subcortical structures show poor
performance on a variety of procedural learning tasks
Priming
Refers to a change in the response to a stimulus, or in the ability to identify a stimulus,
following prior exposure to that stimulus
Example (1)
If you were to see a picture of bicycle handlebars from an odd angle, you would
recognize them as part of a bike faster if you had just seen a typical picture of a
bike
Priming can be perceptual, conceptual, or semantic.
Acts within the perceptual representation system (PRS)
The structure and form of objects and words can be primed by prior experience,
and the effects persist for months
Involves stimuli that have similar forms
Example
The word "goat" will evoke a faster response when it is preceded by the
word "boat" because the two words are perceptually similar.
Conceptual priming
Involves a stimulus and response that are conceptually related
Example
Words such as "desk" and "chair" are likely to show priming effects
because they are in the same conceptual category.
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Semantic priming
Involves words that are associated in a logical or linguistic way
Example
Responding to the word "banana" more rapidly after being primed with
the word "yellow" is an example of semantic priming.
Short term memory
Limited capacity
Hold information for longer than sensory stores (30s)
Fragile: distraction causes you to forget
Two types
Sensory memory
Information decays very rapidly (within 0.5 seconds)
Information can be erased
Stored in sensory memory just long enough to be transferred to short-term memory
Humans have five traditional senses: sight, hearing, taste, smell, touch
Sensory memory allows individuals to retain impressions of sensory information after the
original stimulus has ceased
The formation of a sensory memory trace is only weakly dependent on attention to the
stimulus
Iconic memory
For visual
was the first sensory store to be investigated with experiments dating
back as far as 1740
iconic memory in humans has a large capacity, but decays very rapidly
Echoic memory
For auditory
Auditory information travels as sound waves which are sensed by hair
cells in the ears
Information is sent to and processed in the temporal lobe
holds information for 2–3 seconds to allow for proper processing
regards to language, a characteristic of children who begin speaking late
in development is reduced duration of echoic memory
Echoic memory is a fast-decaying store of auditory information
In the case of damage to or lesions developing on the frontal lobe,
parietal lobe, or hippocampus, echoic memory will likely be shortened
and/or have a slower reaction time
Working memory
Cognitive system with a limited capacity that can hold information temporarily
important for reasoning and the guidance of decision-making and behavior
Often used synonymously with short-term memory, but some theorists consider the two
forms of memory distinct
Assuming that working memory allows for the manipulation of stored information
Widely acknowledged as having limited capacity
Represents a limited-capacity store for retaining information over the short term
(maintenance) and for performing mental operations on the contents of this store
(manipulation)
Example
We can remember a list of numbers, and we can also add (manipulate) them in our
head by using working memory
Atkinson & shiffrin’s modal (or multi-store) model
Proposes that information is first stored in sensory memory
From there, items selected by attentional processes can move into short-term storage
Once in short-term memory, if the item is rehearsed, it can be moved into long-term
memory
Suggests that, at each stage, information can be lost by
Decay (information degrades and is lost over time)
Interference (new information displaces old information)
Or a combination of the two
Formalized the idea that discrete stages of memory exist and that they have different
characteristics
Strong serial structure
Information coming into sensory memory can be passed to short-term memory and only then into longterm memory
Baddeley’s working memory model
Argued that the idea of a unitary short-term memory was insufficient to explain the maintenance and processing of
information over short periods
Proposed a three-part working memory system consisting of a central executive mechanism for controlling two
subordinate systems
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Phonological loop
Hypothesized mechanism for acoustically coding information in working memory
Studies that asked participants to recall strings of consonants
Letters were presented visually, but the pattern of recall errors indicated that
perhaps the letters were not coded visually over the short term
Participants were apparently using an acoustic code
More likely to replace a presented letter with an erroneous letter having a similar
sound (e.g., t for g)
Rather than one with a similar shape (e.g., q for g)
Might have two parts
Short-lived acoustic store for sound inputs
Articulatory component that plays a part in the subvocal rehearsal of visually
presented items to be remembered over the short term
Visuospatial sketchpad
Short-term memory store that parallels the phonological loop and permits information storage
in either purely visual or visuospatial codes
Studies of participants who were instructed to remember a list of words using either
A verbal strategy such as rote rehearsal
Or
A visuospatial strategy based on an imagery mnemonic
Participants were better on the memory test when they used the visuospatial strategy
Verbal strategy, however, proved better when the participants were required to concurrently track a moving
stimulus by operating a stylus during the retention interval
Free recall experiments
Show serial position curve
Primacy effect
Superior recall of item near begin
Is the beginning
You remember it because that is where you started
For example
A subject who reads a sufficiently long list of words is more likely
to remember words toward the beginning than words in the middle
Recency effect
Superior recall of item near end
Is the finish
You remember the end the best
Is increased when too much information is presented too quickly and is reduced when coupled with
other tasks
With respect to jury memory, allowing note taking could also reduce it
Constructive memory
Prior experience
Has an influence on memory
This is a problem with eye witnesses
How fast were the cars going when they … each other?
Smashed, collided, bumped, hit, contacted
Encoding specificity
State, mood and context have influence on memory
Memory performance is optimal when there is a match in processes/context between learning and
retrieving
Flashbulb memories
Where were you on 9/11
Where were you when you heard trump was elected president of the USA
Emotion
Memory deficits
Amnesia
Anterograde
For events after the injury
Loss of ability to form new memories
No consolidation
Loss of memory for events that occur after a lesion
Inability to learn new things
Retrograde
For events before the injury
Loss of memory for events that happened in the past
No retrieval
Sometimes retrograde amnesia is temporally limited, extending back only a few
minutes or hours
Ribot’s law
More loss of the most recent events (closest to the injury) in
retrograde amnesia
First postulated by Théodule Ribot (French psychologist)
Amnesia can differentially affect short term memory, working
memory or long-term memory abilities
-
Alzheimer’s disease
Amyloid plaques and neurofibrillary tangles in brain
Memory impairment and later general impairment
Starts with episodic memory
Starts with entorhinal cortex
-
Largest risk factor: age (6%>80 y )
Hebbian learning
Associative learning
Cells that fire together wire together
Cells that fire together strengthen synapses
Cells that fire separately loose synapse
Asserts that if a neuron is simultaneously
Little Dictionary:
activated by a pathway with a weak input
and another pathway with a strong input
LTP – long term potentiation
both pathways show LTP and the weak
(potentiate = to strengthen)
synapse becomes stronger
When two weak inputs (W1 and W2) and one
LTD – long term depression
strong input (S1) are given to the same cell
When W1 and S1 are active
EPSP – excitatory postsynaptic
together, W1 is strengthened but
potentials
W2 is not
If W2 and S1 are active together,
W1 is not affected by the LTP
induced from W2 and S1
Hebb’s rule / Hebb’s law
If a synapse is active when a postsynaptic neuron is active, the synapse will be strengthened
LTP
-
-
(E)PSP is increased after presynaptic stimulation
Long term synapse strengthening
Occur in the other two excitatory projection pathways of the hippocampus
Last days or weeks in living animals
Varies in the three pathways
Also takes place in other places of the brain
Amygdala
Basal ganglia
Cerebellum
Cortex
Can be recorded by placing stimulating electrodes on the performant pathway and a recording electrode on a
granule cell of the dentate gyrus
- A single pulse is presented and the resulting EPSP is measured
- Size of the first recording is the strength of the connection before the
LTP is induced
- Then the performant pathway is stimulated with a burst of pulses
- After LTP is induced, a single pulse is sent again and the magnitude of
the EPSP in the postsynaptic cell is measured
- Magnitude of EPSP increases after LTP is induced
- Associative LTP – extension of the Hebbs Law
LTD
-
Long term depression
When the pulses are presented slowly – low frequency pulses – LTD develops
(E)PSP is decreased after presynaptic stimulation
Long term synapse weakening
Occurs at synapses in cerebellar purkinje neurons which receive two forms of excitatory input
One from a single climbing fiber and one from hundreds of thousands of parallel fibers
Decreases the efficacy of parallel fiber synapse transmission
-
LTD has been observed in the visual cortex
Long Term Depression
Proposed to be involved in ocular dominance
Reduces PSP
Types of Learning
Supervised learning
Teacher
Important issues
Where do you get examples with answers?
Which examples are important?
How do you translate an error into a correct answer next time so that it generalizes?
Nature (school, university)
Machines (Articial neural networks (ANN), support vector machines (SVM))
Reinforcement learning
A bit of help (rewards)
Important issues
What is the value of actions for future rewards?
Nature (cookie when you are good)
Machines (Q learning)
Unsupervised learning
All on your own
Important issues
What is shared structure and what is unique?
Principle component analysis (PCA)
Content addressable memories (CAM)
Learning over different timescales
Developmental learning
Perception level just before and after birth
Humans: weeks to months
Shape basic connections in the brain/machine
Learn to process basic stimuli from the environment
Learn invariants
A lot of (but not exclusively) unsupervised learning: Artificial Neural Network
Behavioral learning
At the task level throughout life
Humans: years
Shape more complex/advanced connections in the brain/machine
Learn which cause leads to reward at a later time
Learn credit assignment
A lot of (but not exclusively) reinforcement learning
Evolutionary learning
At the architecture level over generations
Humans: centuries/millennia
Shape the basic architecture of the brain/machine
Learn which brain/machine architecture is fittest
I.e. Does the best developmental learning and behavioral learning
Natural selection, genetic algorithms
Artificial Neural Networks
Computing systems vaguely inspired by the biological neural networks that constitute animal brains
A very crude approximation of biological neural networks
They consist of nodes (neurons, units, …)
A node has input/output
They consist of connection between node
Connections have a weight (synaptic strength)
Learning is changing the connection weights
The input function is (usually) defined as: in = ∑ W *a = W ·a
i
j j,i k
i i
This linear weighted sum is transformed into an activation value by an non-linear
activation function:
Step function
Sign function
Sigmoid function
-
Each connection, like the synapses in a biological brain, can transmit a signal to other neurons
artificial neuron that receives a signal then processes it and can signal neurons connected to it
Node/Unit/Neuron
Receives input from some other nodes, or from an external source and computes an output
Each input has an associated weight (w), which is assigned on the basis of its relative importance to other inputs
Applies a function f (defined below) to the weighted sum of its inputs
Types of general structure
Fully connected
All units to all
Are a type of artificial neural network where the architecture is such that all the nodes
or neurons
In one layer are connected to the neurons in the next layer
Feed-forward
One layer to next
Wherein connections between the nodes do not form a cycle
Was the first and simplest type of artificial neural network
The information moves in only one direction (forward)
From the input nodes
Through the hidden nodes (if any)
And to the output nodes
No cycles or loops in the network
Recurrent
Some back connections
Connections between nodes form a directed graph along a temporal sequence
Allows it to exhibit temporal dynamic behavior
Perceptron
-
Has an input layer and an output layer
Uses the step or sign function
Single-layer, feed-forward network
Because of the step or sign function: binary activation
Supervised learning rule for weight changes
Learning in the Perceptron: Algorithm in words
Calculate the error
What values can this error take, assuming a step function)
If error = 0 then stop
Else adjust the weights
Adjusts weights only if input !=0
Increase weight if error=1
Decrease if error = -1
Perceptron Algorithm:
If error (target output – current output) != 0 then
Weight change = (some small constant) * (error) * (input)
In one go:
Weight change = (some small constant) * (target output – current output= * (input)
Perceptron weight learning rule
∆w = μ(t -a )a = μδ a
ki
k k i
k i
∆w = weight change to node k from node i
ki
a = is output of node i, a of node k
i
k
t = target output for node k
k
δ = error for node k
k
μ = learning constant (usually between [0,1])
The Hebbian weight learning rule:
-
∆w = μa a
ki
k i
Linear separability
-
Multi-layer perceptron
Multi-layer perceptron were hypothesized in the 50’s
There is an obvious problem however
We cannot use our Perceptron learning rule to update the nodes in the hidden layer
Why? We do not know the target output for the hidden notes
-
-
Back-propagation learning (‘back-prop’)
Back-prop can be generalized to any number of layers
It can be shown that the perceptron/backprop learning rule is completely identical to an algorithm called gradient
descent (aka hill-climbing or steepest-descent)
Disadvantages:
Learning might take a long time, and is often depended on initial
Weights (slow and inefficient)
It is a black-box
New(online)learning will overwrite old representations
Cannot find the globally optimal solution (local minimum)
It can be over trained: does not generalize to new examples well
Deep learning
Many layers
Back-prop
Convolutional deep neural nets
Analogous to human visual system
Local connectivity in convolutional layers
Often pre-sets, pre-trained or from unsupervised learning
Fully connected (dense) higher layers
Supervised learning
Really good image recognition
About as good as humans
More and more complex representations in the NN layers
Functions of Attention
Vigilance
Signal detection
Try to detect whether we sensed a signal to take (swift) action
Search
Actively looking for a signal
Selective attention
Actively focus on some information and ignoring other information
Divided attention
Perform more than one task simultaneously and shift attention between them
Attention is the ability to
focus awareness on one
stimulus, thought or action
while ignoring other
irrelevant stimuli, thought or
actions
Signal detection theory
Provides a precise language and graphic notation for analyzing decision
making in presence of uncertainty
Offers a way to analyze many different kinds of decision problems
Sensitivity
Many hits
Few false alarms
Specificity
Many correct rejection
Few misses
Hit, Miss, False alarm, Correct rejection
Explained in the picture
In this case if the tumor is
absent and the doctor
responds yes = false alarm
Search
-
In everyday perception, voluntary attention (driven by our goals) and reflexive attention (driven by stimuli in the
world)
Interact in a push-pull fashion, struggling to control the focus of our attention
Feature (pop-out) search
-
-
One set of experiments
They observed that targets are located more quickly among a field of distracters if the target can be
identified by a single stimulus feature, such as color
Example
A red O among green Xs and Os
Doesn’t matter how many distracters appear in the array
Can demonstrate this relation by plotting participants’ reaction times as a function of the number of distracter items
in the display
Conjunction search
Proposed that while elementary stimulus features such as color, motion, shape, and spatial frequency
Can be analyzed pre-attentively and in parallel within multiple specialized feature maps
Spatial attention is more complicated
Spatial attention must be directed to relevant stimuli in order to integrate the features into the perceived object
Necessary to link the information in the different feature maps so that the target can be analyzed and identified
Feature integration theory
A psychological theory of visual perception
Based on the idea that the visual system can process in parallel elementary
features
Such as color, shape, and motion
Requires spatial attention to bind the features that define an object
Spotlight of attention must move sequentially from one item in the array to another
Similarity theory
Suggests that attention is not drawn to locations but rather to image objects
Search efficiency depends on similarities
Between objects in the scene
Possible targets
Between objects within the scene
Guided search theory
Model of visual attention
Explains how we find out intended target when looking in a crowded visual field
First stage, basic stimuli features are processed simultaneously at all locations across the
visual field
Second, limited-capacity serial stage, processing is more complex and restricted to a
particular item or location based on information obtained in the previous stage
Selective Attention
Cocktail party problem/effect
Imagine yourself at a Super Bowl party having a conversation with a friend
How can you focus on this single conversation while the TV is blasting and boisterous conversations are going on
around you?
Psychologist E. C. Cherry (1953) wondered the same thing while attending
cocktail parties
Selective auditory attention allows you to have a conversation - bar or party
- while ignoring the rest of the sounds around you
Selectively attending
You can perceive the signal of interest amid the other noises
If the person you are conversing with is boring
You can give covert attention to a conversation going on behind
you
While still seeming to focus on the conversation in
front of you
Dichotic listening task
Investigated this ability by designing a cock- tail party in the lab
Normal participants, wearing head- phones, listened to competing speech
inputs to the two ears
This setup is referred to as dichotic listening
Then asked the participants to attend to and verbally “shadow” the speech
Coming into one ear, while simultaneously ignoring the input to
the other ear
Discovered that under such conditions, participants could not
Report any details of the speech in the unattended ear
In fact, all they could reliably report from the unattended ear was whether
the speaker was male or female
Attention, in this case voluntary attention, affected what was processed
propose that attention to one ear results in better encoding of the inputs to the attended ear
-
loss or degradation of the unattended inputs to the other ear
Posner cuing task
Have suggested that this attentional spotlight affected reaction times by influencing sensory and perceptual
processing
The stimuli that appeared in an attended location were processed faster
Than the stimuli that appeared in the unattended location
Enhancement of attended stimuli, a type of early selection
Suggests that changes in perceptual processing can happen
When the participant is attending a stimulus location
Voluntary attention
is our ability to intentionally attend to some- thing, such as this book
a goal-driven process, meaning that goals, knowledge, or expectations
used to guide information processing
Reflexive attention
bottom-up, stimulus-driven process in which a sensory event
maybe a loud bang, the sting of a mosquito, a whiff of garlic, a flash of light or motion
captures our attention
these two forms of attention differ in their properties and perhaps partly in their neural mechanisms
Overt /covert attention
when you turn your head to orient toward a stimulus
whether it is for your eyes to get a better look
your ears to pick up a whisper
your nose to sniff the frying bacon
you are exhibiting overt attention
Key Points
Attention involves both top-down (voluntary), goal-directed processes and bottom-up (reflexive), stimulus-driven mechanisms.
Attention can be either overt or covert.
According to early-selection models, a stimulus need not be completely perceptually analyzed before it can be selected for further
processing or rejected as irrelevant. Broadbent proposed such a model of attention.
Late-selection models hypothesize that attended and ignored inputs are processed equivalently by the perceptual system, reaching a stage
of semantic (meaning) encoding and analysis where selection may occur.
Our perceptual system contains stages at which it can process only a certain amount of information at any given time, what are called
limited-capacity stages which result in processing bottlenecks. Attention limits the information to only the most relevant, thereby
preventing overload of the limited-capacity stages.
Cuing tasks, where the focus of attention is manipulated by the information in the cue, are often used to study the effect of attention on
information processing.
Spatial attention is often thought of metaphorically as a “spotlight” of attention that can move around as the person consciously desires, or
that can be reflexively attracted by salient sensory events.
Anatomy of attention
attention system uses subcortical and cortical
networks within the brain
Interact to enable us to selectively
process information in the brain
Several subcortical structures are relevant to
both attentional control and selection
Superior colliculus in the midbrain and the
pulvinar
Involved in aspects of the control of
attention
In the cortex – several areas that are important
to attention
Frontal cortex
Posterior parietal cortex
Posterior superior temporal cortex
Also include some medial brain structures
Anterior cingulate cortex
Posterior cingulate cortex
Insula
Dorsal Frontoparietal attention network
Goal directed driven control
For unattended salient stimuli
Strongly lateralized to the right
Inferior (ventral) parietal and frontal cortex
Ventral Frontoparietal attention network
Stimulus lateralized to the right
Inferior (ventral) parietal and frontal cortex
(NOT THE SAME AS DORSAL AND VENTRAL PATHWAYS)
Attention deficits
ADHD
Attention deficit hyperactivity disorder
Characterized by
Attention deficits (distractibility)
Hyperactivity (fidgetiness)
Impulsiveness
Mood swings
Short temper
High sensitivity to stress
Impaired ability to make and follow plans
Have occupational difficulties or antisocial behaviors in
adulthood
Careful measurements of ADHD people’s behavior help
clarify our descriptions of the condition
Measurements also enable researchers to quantify improvements that might occur after treatment
People with ADHD have difficulty inhibiting their behaviors
ADHD often runs in families, and twin studies suggest fairly high heritability
Attention to a stimulus is almost synonymous with being conscious of it
Attention or consciousness relates to increased brain activity in the areas responsive to a stimulus
Damage to parts of the right hemisphere produce spatial neglect for the left side of the body or the left side of
objects
Sensory neglect results from a deficit in attention, not sensation
Common diagnosis in the United States
Probably the result of a number of genes as well as environmental influences
Many people with ADHD have mild brain abnormalities, but the pattern is small
and inconsistent
Change blindness
Process of failing to notice a change in some scene, usually because the change
occurred gradually or while the viewer was moving or blinking his or her eyes
If part of a complex scene changes slowly, you probably won’t notice it
You might also fail to notice a quick change that occurs while you are blinking your eyes or moving them
Quickest way to get people to notice the change is to instruct them where to direct their attention within the scene
Change blindness is the process of failing to notice a change in some scene, usually because the change occurred
gradually or while the viewer was moving or blinking his or her eyes
Neglect
-
Opposite of attention is inattention, or neglect
Right now, presumably you are attending to what you are reading, ignoring what you see above, below, or to the
left or right of this page
People with damage to parts of the right hemisphere
Tendency to ignore the left side of the body and its surroundings or the left side of objects
Damage in the left hemisphere does not pro- duce much neglect of the right side
Also, generally ignore much of what they hear in the left ear and feel in the left hand, especially if they
simultaneously feel something in the right hand
Exact location of the damage within the right hemisphere varies, as do the details of what the person neglects
Damage to the inferior part of the right parietal cortex tend to neglect everything to the left of their own body
Damage to the superior temporal cortex neglect the left side of objects, regardless of their location
When a patient with neglect sees a large letter com- posed of small letters, he or she can identify the large letter,
even though neglecting part of it when asked to cross off all the small letters. Also, some- one who neglects the left
hand pays attention to it when it is crossed over the right hand
Automatic and controlled processes
Automatization
Controlled processes can become automatic processes
Example
Learning to drive a car
Can take a long time
Practice effects
Rate of learning slows
The first few practice sessions – much is learned
Over time each session results in less learning
Stroop effect
Delay in reaction time between congruent and incongruent stimuli
Used to create a psychological test
Widely used in clinical practice and investigation
-
Basic task that demonstrates this effect
Occurs when there is a mismatch between the name of a color
"blue", "green", or "red"
And the color it is printed on
The word "red" printed in blue ink instead of red ink
When asked to name the color of the word it takes longer and is more prone to errors when the color of
the ink does not match the name of the color
Attentive robots
Example
BeoBot
Attentional SLAM
Autonomous city explorer
Robots that use a computational attention system to direct their focus of attention to parts of the sensory input which are
currently of most potential interest
Social robots
Autonomous robot
Interacts and communicates with humans or other physical agents
By following social behaviors and rules attached to its role
Research design
Correlational
-
Just measure variables as they occur
Used to determine if there is an association
You can never infer a causal relationship
-
Involves a manipulation of one variable
Keep other variables constant
Can show a causal relationship
Experimental
Computer modeling
-
Simulate models of cognition inside the computer
Use them to generate testable prediction
Most well-known models are based on connectionist approach (ANNs)
As computers become more powerful, so do the models
Great as a testbed for studying theories about human cognition
But:
Models always simplify
George P. Box: “All Models are wrong, but some are useful”
Some models are not biological plausible
Some models are too complex they fit almost any data, and can generate almost any desired behavior,
but generalize poorly
Always many different models that can generate can same behavior
John von Neumann: “Give me 4 degrees of freedom and I will fit you and elephant, give me 5
and I will have it wave its trunk at you”
Symbolic modeling
Often serial and abstract processing
Example
Expert Systems
Connectionism
Parallel and distributed processing
Example
ANN’s
Still both at Marr’s algorithmic level
Realistic neuronal modeling
IBM Blue Brain
The EU Human brain project
Much closer to Marr’s implementational level
Eventually: neuromorphic computing
Braitenberg vehicles
We see that there is no difference in how the two models process information, but only a difference in their
patterns of connectivity
The point of Braitenberg’s example is not to model a behavior; rather, it represents how a single computational
change – from crossed to uncrossed wiring – can yield a major behavior change. When interpreting such a
behavioral difference, we might postulate extensive internal operations and representations
Pro’s and Con’s
Advantages
Can be safer and cheaper than the real world.
Able to test a product or system works before building it
-
Can use it to find unexpected problems
Able to explore ‘what if…’ questions
Can speed things up or slow them down to see changes over long or short periods of time
Disadvantages
Mistakes may be made in the programming or rules of the simulation or model
The cost of a simulation model can be high
-
The cost of running several different simulations may be high
-
Time may be needed to make sense of the results
-
People’s reactions to the model or simulation might not be realistic or reliable
Lesion Studies
-
-
-
-
Structural Imaging
CT / CAT
-
Provided key insights into the relationship between brain and behavior
Study of damage to the human brain allows us to understand functions of
certain parts
If something is damaged, the changes in behavior are often linked to the
damaged region
Fundamental concepts
Left hemisphere dominant role in language
The dependence of visual functions on posterior cortical regions
Careful with interpretation of results
Which functional area
Can have an effect on other regions
It is not a normal, healthy brain…
Dissociations
No dissociation
One lesion impairs A and B
Example
Lesion in parietal cortex impairs visual attention and speech perception
Single dissociation
One lesion impairs A and B, other only B
Example
Lesion in parietal cortex impairs visual attention and speech perception
And lesion in temporal cortex impairs only speech perception
Double dissociation
One lesion impairs only A, other lesion only B
Example
Lesion in parietal cortex impairs only visual attention
And lesion in temporal cortex impairs only speech perception
Pro’s and Con’s
Pros
gives inside to damage
Cons
Brain is complex
Damage to one part could affect another
Skewing results
Results in a non-healthy brain
Not a dependable source of research
CT = Computed Tomography
Uses X-Rays
Different tissues absorb different amounts of X-Rays
Shows contrast between tissue
Is radioactive
Causes damage
Not always feasible for prolonged study
Structural MRI
MRI = Magnetic Resonance Imagining
MRI system
Causes spinning atoms in the field to align to magnetic North/South
Then, a radio wave is beamed into the field, causing unmatched atoms to
align in opposite directions
When the radio wave is turned off, atoms realign, releasing energy
We can measure this energy
Magnet (1.5T – 9.4T)
Higher number = higher magnetic field
Why higher fields?
The higher the rating, the higher the magnetic field
Which results in more accurate readings
Gradient coils
Creates a secondary magnetic field
In a predictable manner
Allows us to alter the resonant frequency of certain atoms
Radio frequency coil
Beams radio waves into the field
Protons / spins
Spinning atoms
What we measure in an MRI
Larmour frequency
The frequency of the radio pulse
Determined by gyromagnetic ratio: Hz/Tesla
Gyromagnetic ratio
Hertz/Tesla
T1 weighted, T2 weighted, T2* weighted
Different relaxation times (of the spins realigning)
Give different contrast, enhancing images
Diffusion MRI / DTI
Uses the diffusion of water molecules
To enhance contrast in MR Images
Anistropic diffusion
Directional diffusion within the brain
Useful for determining structures in the brain that restrict the flow of water
Such as myelinated axons of nerve cells (affected by multiple
sclerosis)
Pro’s
-
Gives us increased clarity in the flow of water throughout the brain
-
Doesn’t tell us much about injuries/lesions
Con’s
Functional Imaging
Single cell recording
Famous experiment by Hubel and Wiesel. Cells in the V1 (see visual cortex)
respond in a specific manner
Pro’s
Gives very high resolution
Con’s
Highly invasive
Does not give the whole picture
EEG
-
EEG = Electroencephalogram
Measures overall brain activity over time
High temporal resolution
Uses electrodes to measure activity of groups of neurons that fire in parallel
ERP
ERP = Event – related potential
Once an event occurs, we can measure the brain activity as it happens
ECoG
Electrodes are placed directly on the surface of the brain
Much more invasive, but less noisy
Pro’s
Very cheap
Very high temporal resolution
Con’s
Very poor spatial resolution
Very noisy
Impossible to detect
MEG
-
Magnetoencephalogram
Measures same activity as EEG
Less mobile
More accurate in location
Pro’s
More accurate in spatial resolution (contrast)
Con’s
Less mobile, less practical
Time-frequency analysis
We don’t always see everything
Do the same thing over and over again
Average results
-
Positron Emission Topography
Measures brain activity through a tracer
Substance given to patient
Sits in bloodstream
Subtraction method
Allows us to determine very specific locations in
the brain
Using subtraction of a control vs affected image
Pro’s
You can measure what you trace depending on
the substance given
Con’s
Radioactive substance must be imbibed
Has been replaced by better methods
Experiments are short (radioactive decay)
Very expansive
-
fMRI = functional MRI
goes beyond subtraction method
relies on the general linear model
PET
fMRI
BOLD, oxyHb and deoxyHb
Oxygenated vs Deoxygenated Hemoglobin (Hb) has different resonant
magnetic frequencies
BOLD = blood Oxygen Level Dependent responses
Gives us an insight to mixture of blood flow/volume in brain
Block design & event-related design
Create an event and measure the response over time (2-3 seconds)
Rt-fMRI, BCI & Neurofeedback
Real-Time fMRI, record results as they happen
BCI = Brain Computer Interface, allows us to control computers via thought
Neurofeedback feeds brain activity back to the subject. Subject can “train” their thoughts to control
devices via BCI
Pro’s
-
Very high spatial resolution
Relatively high temporal
resolution
Non-invasive
-
Temporally limited
-
Con’s
Spatial & temporal resolution
Spatial = location
Temporal = time
Relative resolutions of modalities
Log size
Log time plot
Methods to perturb function
Perturbing function is altering the function of the brain, whether through drugs, stimulants, or otherwise
Because damage to the brain does not necessarily tell you what the function of the damaged portion does
Removing the spark plug from an engine does the same thing as running out of fuel, but they’re two different things
entirely
Focusing on more localized, controlled “perturbation”
Pharmacological studies
There are certain studies that introduce certain types of chemicals, or drugs, known as agonists
Which act like neurotransmitters and mimic/increase neurotransmission
Antagonists
Which bind to cell receptors and block or somewhat dampen neurotransmission)
These studies allow us to study the direct effects of certain neurotransmitters or other chemicals on
cognitive function
TMS
-
Transcranial magnetic stimulation
A large coil generating a strong magnetic field is placed on the skull and causes certain neurons to fire
The mechanism is poorly understood, though the applications are many
Pulsed tms
Pulsing the magnetic field
Able to time any given stimulus with the tms pulse to prevent certain actions from happening,
such as pulsing in the visual cortex between 70-130ms after the subject is shown a certain
letter in the alphabet, preventing them from identifying and naming the letter
Repetitive tms
Performing tms to specific regions of the brain repeatedly over many sessions
Allows certain patients with physiological or psychological disorders to experience temporary
relief
The more often and prolonged a session is, the longer the residual benefit
tDCS
-
Transcranial direct current stimulation
An anode and cathode are placed onto the scalp
Neurons underneath these terminals become depolarized
Allowing them to become much more excitable and therefore more likely to trigger an ap when a specific
stimulus occurs
Genetic manipulation
One of the greatest scientific challenges of today is in the manipulation of genes
To determine the eventual outcome of human development
The human genome project was able to successfully map the entire human genome
The challenge lies within decoding all of the information, and determine which genes lead to which type
of development
Such as which genes lead to the development of brain tissue vs muscle tissue, etc
Knockout procedures
A type of experiment on animals where scientists “knock out” a specific gene
Let the specimen develop otherwise normally to see if they can’t detect what changes their
manipulation leads to
Example
Certain types of mice with “knocked-out genes” were unable to develop their cerebellum
fully, leading them to develop poor motor control
Language & Linguistics
Language is uniquely human
There is a lack of an upper bound on the number of grammatical sentences in a language
Language is recursive
Language structure is the same all over the world
Human language acquisition is the same all over the world
Language is learned from imperfect environments
Grammar
Refers to the structural rules that govern the composition of words, phrases and sentences in a particular natural
language
Syntax
-
Rules that tell us how to organize words (grammar)
Phoneme
Smallest unit of speech
Grapheme
Smallest unit of written language
Semantics
Meaning of language
Semantic relationships between words are ab organizational
principle of the mental lexicon
Morpheme
Smallest unit with meaning
Lexicon
-
Mental store of word information
Model for the lexicon: semantic network
Words and their associative connections
Strongly semantically or associatively related words are close
Semantically related: similarly colored
Associatively related: connected
Prosody
-
Rhythm and pitch of speech
Pragmatics
Knowledge of social rules
Language acquisition
Language is special to humans
Animals communicate, but no advanced language
We learn language despite (motherese)
Motherse = simplified and repetitive type of speech, with exaggerated intonation and rhythm (often used by adults when
speaking to babies
Human language acquisition is the same all over the world
Stages
Cooing
Babbling (6 months of age)
One- word utterances (1 year of age)
Two-word utterances (1-3 years of age)
Basic adult structure
Overextension error
Use of wrong semantic word
Example
Everything with four legs is a doggie
Irregular verb errors
They first get it right: sing – sang
Later on, they get it wrong: sing – singed (overgeneralization)
Eventually they get it right again: sing – sang
Irregular past tense is acquired associatively and regular as rule based
Critical period
There seems to be a critical period for language acquisition
As you get older, you may learn a language, but never with the same mastery as you did when you were younger
Anatomy of Language
Lateralization
Language is left lateralized
Left peri-sylvian language network
Peri-sylvian language network
Inferior frontal cortex
Broca’s area
Inferior parietal lobule
Superior temporal gyrus
Wernicke’s area
Arcuate fasciculus
Aphasia
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Brain damage in the language areas often leads to Aphasia
Deficits in language comprehension and production
Even though articulatory mechanisms are intact
Very common after a stroke (40%)
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Almost all strokes of the left hemisphere lead to transient aphasia
Broca’s aphasia
- Also called anterior aphasia or expressive aphasia
- Damage of the Broca’s area
- Mainly deficits in speech production
- Also, comprehension deficits related to syntax (agrammatic aphasia)
- Example
"Me ... build-ing ... chairs, no, no cab-in-ets. One, saw ... then, cutting wood ... working ..."
Wernicke’s aphasia
- Also called posterior aphasia, receptive aphasia
- Damage of Wernicke’s area
- Mainly deficits in speech comprehension
- Also production deficits related to semantics (speak fluent but nonsensical)
- Example
Examiner: What kind of work have you done?
W. Patient: We, the kids, all of us, and I, we were working for a long time in the ... you know ...
it's the kind of space, I mean place rear to the spedawn ...
Conduction aphasia
Damage of arcuate fasciculus
Disconnection syndrome
Mainly production deficits
Problems producing and repeating speech
Key Points Anatomy of Language:
Anomia is the inability to find the words to label things in the world. It is not a deficit of knowledge.
- A left-hemisphere network involving the frontal, parietal, and temporal lobes is especially critical for language pro- duction and comprehension.
- The right hemisphere does have roles in language, especially in processing the prosody of language.
- Language disorders, generally called aphasia, can include deficits in comprehension or production of language resulting from neurological damage.
- Patients with Broca’s aphasia have problems with speech production, syntax, and grammar, but otherwise comprehend what is said or written fairly well.
- The lesions that produce Broca’s aphasia may not be limited to the classically defined Broca’s area in the left inferior frontal cortex.
- People with Wernicke’s aphasia have severe comprehension deficits but can produce relatively fluid speech; it is, however, rather meaningless. Originally linked
to damage solely in Wernicke’s area (the posterior superior temporal gyrus), today Wernicke’s aphasia is also linked to dam- age outside the classic Wernicke’s
area.
- Aphasia can also result from damage to the connection between Wernicke’s and Broca’s areas (the arcuate fasciculus). Conduction aphasia is the disorder that
results from such damage, and people with this type of aphasia have problems producing spontaneous speech as well as repeating speech.
Language Comprehension
Semantics
Denotation
Explicit or direct meaning
Connotation
Associated or secondary meaning
Can be something suggested or implied by a word or thing
Syntax
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Refers to the way in which words in a particular language are organized into grammatically
permitted sentences
Phrase structure grammar
Is a type of generative grammar in which constituent structures are represented
By phrase structures rule or rewrite rule
Chomsky’s transformational grammar
Part of the theory of generative grammar
Especially of natural languages
Considers grammar to be a system of rules that generate exactly those
combinations of words that from grammatical sentences in a given language
Perceptual Analysis
In order to understand spoken words, the listener has to decode the acoustic input
Result of this acoustic analysis is translated into a phonological code
Because through phonological code is how lexical representations of auditory words forms are stored in
the mental lexicon
After phonological format – lexical representations in the mental lexicon that match the auditory input can be
accessed
The best match can be selected
Selected word – includes grammatical and semantic information stored in the mental lexicon
Helps to specify how the word can be used in the given language
Spoken word recognition processing proceeds anteriorly in the superior temporal gyrus (STG)
Phenome processing appears localized to the left mid-STG
Integration of phonemes into words appears to the left anterior STG
Processing short phrases appears in the most anterior locations of superior temporal sulcus (STS)
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Invariance Problem
Refers to the challenge that listeners face when confronted with acoustic variability in speech sounds
As they attempt to map these sounds to few phonological categories
Coarticulation & segmentation problem
Problem of text segmentation that occurs in some languages which are (traditionally) written without
inter-word spaces
Like Chinese and Japanese
Compared to writing system which indicate speech segmentation between words by a word
divider (space)
Reading
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Words can be symbolized in writing in three different ways: alphabetic, syllabic, and logographic
Involves the visual analysis of horizontal lines, vertical lines, closed curves, open curves, intersections, and other
elementary shapes
Pattern recognition
Selfridge’s pandemonium model
Consists solely of stimulus-driven
(bottom-up) processing and does
not allow for feedback (top-down)
processing
Mclelland & Rumelhart’s connectionist model
Proposed a computational model
that has been important for visual
letter recognition
Assumes three levels of
representation:
A layer for the features
of the letters of words
A layer for letters
A layer for the
representation of words
Permits top-down information (i.e.,
information from the higher
cognitive levels, such as the word
layer)
Influence earlier processes that happen at lower levels of representation (the letter
layer and/or the feature layer)
Lexical Analysis
Lexical access
Refers to the stages of processing in which the output of perceptual analysis
Activates word-form representations in the mental lexicon
Including their semantic and syntactic attributes
Lexical selection
Is the next stage where the lexical representation in the mental lexicon that best matches the
input can be identified (selected)
Lexical integration
Integrates words into the full sentence, discourse, or larger context
Grammar and syntax are the rules by which lexical items are organized in a particular
language
To produce the intended meaning
we begin by considering the mental lexicon, the brains store of words and concepts and ask
how it might be organized and how it might be represented in the brain
Speech Production
Slips of the tongue
Slips of the tongue help us to make models of language
Anticipation
Bake my bike
Perseveration
Cold curkey
Substitution
He is going up town
Reversal/Spoonerism
The lord is shoving leopard
Levelt’s model
Predicts the following result when someone is presented with a picture of a flock of goats
and is asked to name them
Conceptual preparation
First the concept that represents a goat is activated
Concepts related to the meaning of goat are also activated
Lexical encoding
Lexical selection
Rules governing which lexical items may appear in which sentence
structures
Morphological encoding
Contains both phonological information and metrical information
Metrical information – information about the number of syllables in the word and the stress
pattern
Phonological encoding
Ensures that the phonological information is mapped onto the metrical information
Articulation
Involves the posterior parts of Brocas area (BA44)
Studies showed bilateral activation of motor cortex, the supplementary motor area (SMA) and the insula
Can computers understand language?
Turing test
Alan Turing
Test of a machines ability to exhibit intelligent behavior equivalent to that of a human
ELIZA
An early natural language processing computer program
Created to demonstrate the superficiality of communication between humans and machines
Simulated conversation by using a “pattern matching” and substitution methodology that
gave users an illusion of understanding on the part the program
Had no built-in framework for contextualizing events
WATSON
Question answering computer system capable of answering questions
Combines artificial intelligence and sophisticated analytical software for optimal performance
as a “question answering” machine
Deductive Reasoning
Conclusions follow certainly from the premises
Premises
A statement concerning only facts
Do not have to be true, but rather empirical
“some students pass this course”
Conclusion
“some students study for this course”
Quantifier
A word or statement concerning the premise that give it specific content
“Some student study for this course”
Atmosphere effect
The atmosphere of a statement, or the context in which it is given
Can influence the user’s ability to reason
“All students drink alcohol, therefore all students are alcoholics”
Categorical reasoning
Consist of a premise followed by a quantifier
Conditional reasoning
Contains a premise and conclusion
Syllogistic reasoning
The most common form of deductive reasoning
Consists of premises followed by a conclusion
Modus ponens (Method of affirming)
If P2 = p, then the conclusion = p
Modus Tollens (Method of denying)
If P2 = !P, then the conclusion = !P
Denying the antecedent error
P => Q: if not P, then not Q
This is incorrect
Affirming the consequent error
P => Q: Q is true , therefore Q is true
This is incorrect
Wason selection task
A common logical task
Example
Four cards are on the table, with a letter on one side and a number on the other. Tell the
participants an arbitrary rule, and ask them which card they must flip over to test if the rule is
correct
This is a difficult task when implemented in a formal manner, but when it becomes practical, the success
rate skyrockets to about 75%
Inductive Reasoning
From a large body of evidence, we make conclusions that are probably true
Based on observation, yet the hypothesis cannot be officially proven (must use statistics to prove the probability of being true)
Heuristics & Bias
Heuristics are “rules of thumb”
Availability heuristic
We are biased by our experience with the availability of experiences, by recentness and frequency
Representativeness heuristic
We are biased by the way information is presented to us
Even if the information is obviously correct/incorrect
The manner in which it is presented is critical in our reasoning techniques
Expertise
Three stages of skill acquisition:
Cognitive stage
The processes of developing declarative encoding
Associative stage
Errors eliminated and good actions strengthened
Autonomous stage
No more thinking required
Automatic actions
Power law of learning
𝑇 = 𝑎𝑃 %&
T = Time needed to solve a task
A = Learning constant
P = Practice
b = learning constant
Tactical learning
Learning the sequence to solve a particular problem or perform a task
Strategic learning
Learning to organize the solution differently
Deliberate practice
Must be motivated to learn not just reproduce
Given feedback on performance
Focus on improving performance
Intelligence
IQ test
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Began as a way to monitor childhood development
Compared to an average
Relative/Normative
Relative
Relating mental age to chronological age
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Subtests
Factors
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Normative
Relating scores to the average score
Modern IQ tests are normative
Spatial, verbal, non-verbal, reasoning, short/long term memory tasks
Only one: g (IQ)
Spearman’s model
Multiple factors
Thurstone’s Model (3-5)
Guilford (120+)
Crystallized & Fluid intelligence
Fluid Intelligence: ability to solve new problems and identify patterns
Crystallized intelligence: ability to use learned knowledge and experience
Flynn effect!
Every two years the general IQ goes up by 1 point
Construct validity
The debate over whether the structure or “construct” of the IQ test adequately tests true intelligence
Or if there is some form of bias in this form of evaluation
IQ tests biased towards who are not blind etc.
Artificial Intelligence:
Consistent
A formal system is consistent if it does not contain a contradiction
P and not P are both true
Complete
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A formal system is complete if all the statements can be made in a system are “decidable” or evaluable within that
system
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An artificially intelligent system
Developed by Medin, Wattenmaker, and Michalski
Was Heuristic (rule based search) using symbolic descriptions
Medin, Wattenmaker & Michalski (1987)
Categorization algorithm
An algorithm that categorizes decisions and their outcomes
Then decides its next move based upon the most rewarding outcome
Category validity
Humans tend to category validity
Cue validity
Cue Validity determines the value of a certain input/decision
Based upon its probability of occurring or existing within a certain category
Based on its particular feature, or cue
INDUCE tends to cue validity
Product- Process- equivalence
DEEP BLUE
Another artificially intelligent agent devised by IBM designed to play Chess
Deep Blue beat the reigning chess grand master in 1997
The person it beat accused IBM of cheating, which they denied, fucked off, and retired Deep
Blue
Dijkstra
Asking a computer whether it can think is like asking if submarines can swim
INDUCE
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Consciousness
Core consciousness
Brainstem
Is the “star player” in the brain
Houses some of the most essential brain functions for life
Controls breathing, automatic responses in the face, neck and torso
Is the channel between the brain and the PNS
Thalamus RAS
RAS = Reticular activating system
Modulates arousal and attention through direct connections to the cortex
Extended consciousness
Cerebral cortex
Sense of self, memories and expectations
Clinical perspective
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Sleep
What is consciousness?
We are able to react purposefully to external stimuli and are awake
Measured on a quantitative level
Impairments
Somnolence
Abnormal sleepiness
Acoustically arousable
Sopor
No sponatous movements
Reaction to pain stimuli adequate
Coma
No reaction to any sort of stimuli
Pain, sound, visual – nothing
You can recover
(Brain death)
The body may be alive
CNS (Central Nervous system) is unresponsive
Vegetative state
Includes failure to produce any purposeful voluntary behavior
Unconscious, reflexive responses, opening eyes
Unresponsive to stimuli (except pain)
Abnormal sleep/wake cycles
“normal behavior may persist
Grinding teeth
Smacking lips
Transient: temporary
Persistent: continuous
Locked-in syndrome
Patient is actually fully conscious
Cannot move or make themselves clear to their environment
Can make vertical eye movement or close eyelids
Use EEG or Real Time fmri to communicate
Terri Schiavo case
Car accident
Left in persistent vegetative state
Fought in court over taking her off life support
Was taken off and passed away
Arguments were about whether she would ever recover
Stages
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Sleep comes in stages and fluctuates between different states
Brain activity can be monitored via EEG (Electroencephalography) and EOG (Electrooculography)
Stage 1
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Light sleep
Where the person drifts in and out of consciousness
Can be awakened easily
Prepares the body for deeper stages pf sleep
Stage 2
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Eye movements stop
Brain activity lowers except for very rapid spikes in brain activity
Sleep spindles
Rapid spikes or spindles (visible on an EEG)
During sleep stage 2
Generated in the Thalamus
It is believed that is an automatic “test” the brain performs, trying to determine certain functions of
certain brain structures when asleep
K-complexes
Singular, large spike in brain waves (visible on an EEG)
Largest healthy spike in brain activity
It is believed that these perform the function of initiating/performing memory consolidation
Stages 3&4
This is deep sleep
“Deeper than those conversations you have at 4AM after partying all night”
Normal brain activity is extremely low, expect the brain emits strong Delta Waves
Slow wave sleep
Where the brain exclusively produces delta waves
These are slow, large brain waves that are believed to be signs of neural development and
reconsolidation/orientation
These waves are strongest in people under the age of 40
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REM/ paradoxical sleep
REM = Rapid Eye Movement
Clear sign of deep sleep
The period when the most vivid dreams occur
Increased activity in the
Pons/Reticular formation
Temporal and parietal cortex
Decreased activity in the
Visual, motor and prefrontal cortex
Muscles are immobilized
Dreaming
“what you are doing right now when you imagine being at the beach instead of school”
Eye movements and EEG
The eye and its movements heavily affect EEG readings
Can lead to distortion
Allows to detect Rapid Eye Movement in sleep
Sleep cycles through the stages
Cycle change through the night
We drift in and out of sleep cycles throughout the night
Reaching stage 4 early during sleep
Slowly drifting
Back down to 2 and 3
Stage 1 before waking up again
Functions of sleep
Save energy
Restore the brain
Muscle repair
Cell repair
Tissue growth
Protein synthesis
Release of many of the important hormones for growth
Sleep allows the body to repair and replete several cellular components that are needed for physiological functions
Memory
Strengthens and weaken connections
Consolidate memories obtained that day
REM sleep functions
Function not entirely understood
Used for memory maintenance
NN of REM: memory ‘cleanup’
Neural Network model of REM
Echidna does not dream
Echidna does not dream
Has an especially large cortex
Binding problem
What is the problem
We don’t understand how all of the input from our senses, our memories and all parts of the brain bind
together
To form one cohesive experience
Clinical neuropsychological evidence for the binding problem
Apperceptive agnosia
Shapes
Spatial grouping
Achromatopsia
Colors
Feature integration
Prosopagnosia
Faces
Part binding
Semantic dementia
Semantic
Conceptual binding
Simultanagnosia (Balint‘s syndrom)
Location binding
Akinetopsia
Serial
Event binding
Feature integration theory
Binding is achieved in temporal dimension
Via synchronous oscillation of neurons
Binding by neuronal synchronization
Synchronous oscillation is rhythmic repetitive neural activity in the CNS
Neurons are firing at repeated intervals
Creating oscillations in brain activity
Free will
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What you think you have
Readiness potential
During a conscious task
Your muscles are “ready” about 1000ms before you actually move them
Libet’s experiment
Determine the relationship between Readiness potential and the subjective experience of free will
Turns out we might not have free will
but rather the inhibition to stop automatic responses
RP
starts early
W
Will to move
W-S
Corrected “will to move”
EMG
Automated muscle activity
Soon’s fMRI experiment
Showing a stream of letters every 500ms
the user can press a button whenever desired
you must remember the letter displayed whenever the button was pressed
Determined that users were only able to decode their decision AFTER they performed it
Qualia
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Individual, separate instances of subjective, conscious thought
Chalmers: easy problem & hard problem
A thought experiment posed by David Chalmers
where the experience of conscious thought poses two types of problems, easy and
hard problems
Easy problems
problems - represented or explained by some behavior, habit, or function, such as
controlling behavior, deliberately paying attention, the ability to recognize things in
our environment
can be explained, regardless of how rigorously, by observance of natural
phenomena
Hard problems
problems that have an inherent subjective aspect, such as “why are we able to
contemplate our own existence?”
these questions are not fundamentally observable and therefore “hard” to prove.
Note: The Hard/Easy problem experiment has been discredited and considered out of date with modern psychological understanding.
Nagel What it’s like to be a bat
Speculation about what it’s like to be a bat
Our experiences would be completely different
Because they perceive “visually” via echolocation
Inverted Spectrum Problem
The hypothetical thought experiment where two people experience the “same” color
But in reality, see it differently
We both know what red is, but do we see red the same way
Originally posed by John Locke
Mary the color scientist
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Thought experiment where a hypothetical scientist “Mary” experiences her whole life in a
black and white room
Studies the science of visual perception using only black and white shading
She knows what shade of “grey” is red, and which is blue
The experiment poses the question: “Will she learn anything new by leaving her room and
experiencing actual color for the first time?”
Posed by Frank Jackson