Sensation & Perception
• Ch. 2: Physiology of Perception
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
• Main topics
–
–
–
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Neurons
Vision
Transforming light into electricity
Pigments and perception
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Anatomy Lesson by Dr. Nicholaes (painted by
Rembrandt Harmenszoon vanch 2Rijn in 1632)
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Some brief history
• “Anatomy of the Brain” by Thomas Willis
(1664)
• Oxford physician
• The first major work on the brain.
• Present the results of dissections of a human brain.
• Staining
• By Gamillo Golgi (1873)
• Injecting dyes into the nervous system
• Enabled the visualization of neurons
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• A nerve cell (neuron) shown by the Golgi
method.
http://en.wikipedia.org/wiki/Image:GolgiStai
nedPyramidalCell.jpg
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• Doctrine of specific nerve energy
– By Johannes Mueller (1842)
– Our perceptions depend on “nerve
energies” reaching the brain and that the
specific quality we experience depends
on which nerves are stimulated.
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Basic structure of the brain
• Modular organization
– Specific functions are served by specific areas of
the cortex.
– Primary receiving areas:
• Occipital lobe (seeing)
• Temporal lobe (hearing)
• Parietal lobe (touching)
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Source: Kandel et al., 1994ch 2
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Human brain
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Neuron
• Key components:
– Cell body, dendrite, axon, and synapse
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Neuron I
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Neuron II
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Neurons
Dendrites
Cell body
Axon
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Perception involves
Inform
ation
• Transduction and neural processing
• And then behavior
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Behavior
/action
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Transduction
–Different types of information (air
vibration, light energy) is transformed into
a common neural language in the brain 
neural information
– this process is called
“TRANSDUCTION.”
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Transduction: Examples
– Touching a mouse, open a program, typing some
words.
– Driving a car
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Neural energy
• What is neural energy?
– It is basically a conversation between neurons.
• Conversation? They talk to each other?
• Yap.
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How do neurons talk to each
other?
• Neurons talk to each like a computer does.
• Neurons talk to each other by sending
electrical signals.
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How so?
This figure shows the high concentration
of positively charged sodium (NA+) and
the high concentration of positively
charged potassium (K+).
A neuron is immersed in liquid rich in ions
(molecules that carry electrical charge).
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Ion?
•
An ion is an atom or group of bonded
atoms which have lost or gained one or
more electrons, making them negatively
or positively charged.
•
A negatively charged ion has more
electrons in its electron shells than it has
protons in its nuclei.
•
Atom?
•
An atom is the smallest particle still
characterizing a chemical element; it is
composed of various subatomic
particles:
•
Electrons have a negative charge; they
are the least heavy (i.e., massive) of
the three types of basic particles.
•
Protons have a positive charge with a
free mass about 1836 times more than
electrons .
•
Neutrons have no charge, have a free
mass about 1839 times the mass of
electrons.
A positively-charged ion has fewer
electrons than protons.
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• (Wikipedia.org)
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Neurons talk to each other
electronically by sending chemicals
(neurotransmitters) from one
neuron to other neurons.
Neurons are not directly attached
but are connected indirectly at a
juncture called
“synapse.”
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Synapse
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Neurons (schematic Illustration)
Dendrite
When an electric
signal reaches at the
end of the axon of a
neuron, that neuron
releases
“neurotransmitters”
Axon
Synapse
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Synapse and neurotransmitter
Dendrite
Axon
The
neurotransmitters
reach a terminal
of a dendrite of
the other neuron,
and change the
neuron’s resting
potential.
Synapse
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Resting potential
The electrical charge when a
neuron is at rest is called “resting
potential.”  -70millivolt
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Dendrites collect
electrical signals
from other neurons.
axon
dendrites
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Dendrites forward
these signals to the
cell body.
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+
+
axon
+
When the signals
that gather at the
cell body exceed
a threshold, the
axon triggers a
new signal (i.e.,
spike).
dendrites
+
Firing (spike)
No Firing
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Accumulation of signals
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Neurotransmitters can send
positive or negative signals.
Dendrite
Axon
Synapse
Neurotransmitters can
open positive or
negative gates.
Some
neurotransmitters
open positive
gates.
Some
neurotransmitters
open negative
gates.
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axon
axon
dendrites
dendrites
Basically there are two types of neuro-transmitters.
One that sends excitatory (+) signals (transmitter), and
the other that sends inhibitory (-) signals.
So, the excitatory neurons enhance the activity of
other neurons; the inhibitory neurons suppress the
activity of other neurons.
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Demonstration
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Activities of neurons can be
schematically shown as
a1 a2 a3 a4
The firing rate of neuron
B is determined by the
activation sent by neurons
a1-a4.
B
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Summary
• A neuron consists of dendrites, a cell body
and an axon.
• Neurons are not directly attached but are
indirectly connected by synapses.
• One neuron sends an electrical signal to
another neuron by releasing
neurotransmitters.
• Some neurons send excitatory signals (+);
others send inhibitory signals (-).
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What does this tell? (1)
• Perception can be examined by the activity of
neurons.
– When we are perceiving something, some
neurons are firing.
When we see a picture like
this, neurons that respond
to different colors, shapes,
texture,… are firing
together.
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Bridging the activity of neurons
and behavior (perception)
• Single cell recording
• ERP (Event related potential/evoked
potentials)
• PET (Positron Emission Tomography)
• fMRI (functional Magnetic Resonance
Imaging)
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Single cell recording
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ERP
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Biofeedback
Neurofeedback for attention deficit
disorder
http://www.youtube.com/watch?v=2v
UG6BDA8wI
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PET & fMRI
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fMRI
Source: Kandel et al., 1994
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fMRI Setup
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fMRI Experiment Stages:
Anatomicals
4) Take anatomical (T1) images
•
•
•
high-resolution images (e.g., 1x1x2.5 mm)
3D data: 3 spatial dimensions, sampled at one point in time
64 anatomical slices takes ~5 minutes
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Source: Jody Culham’s fMRI for Dummies web site
PET (Normal resting pattern)
Source: Kandel et al., 1994ch 2
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PET (visual & auditory
stimulation)
Source: Kandel et al., 1994ch 2
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• fMRI and a lie detector
• http://www.youtube.com/watch?v=Cwda
7YWK0WQ
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TMS
• Transcranial magnetic stimulation
– Disrupt the electrical activity of neurons in a
targeted area by a strong magnetic field (4:15)
– http://www.youtube.com/watch?v=XJtNPqCjiA
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ERP, PET, &MRI
• Subjects carry out some psychological tasks
(e.g., visual perception)
• Trace neural activities of the brain.
• Identify the brain location in which the
psychological function takes place.
• Bridge psychological functions and their
brain locations.
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Visual perception
• What is the difference
between (a) & (b)?
(a)
• What is going on in your
head when you see (a)
versus when you see (b)?
(b)
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How about this?
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What’s going on?
• When you see the square, what’s going on?
• How do you find out?
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• In terms of the activity of neurons,
what is the difference between
A and B ?
Any guess?
B.
A.
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Measuring the
electrical activity of a
neuron directly by
inserting a thin needle
into animal brains.
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The frequency of
action potential
0
t
0
t
The number of
action potential
emitted by a
neuron is
correlated with
Time
the intensity of
the stimulus.
Time
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t
Time
Questions: What happens to B?
0
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Questions: What happens to B?
Excitatory
Inhibitory
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Specificity coding vs. Distributed
coding
• How are objects represented in the visual
system?
• Think about human faces. Every face is
different. So do we need an infinite number
of neurons to represent individual faces?
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Specific coding?
• A single neuron responds
to each face?
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Specific
• A single
neuron coding?
responds
to each face?
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Neurons in the
hippocampus respond
specifically to an
individual person, such
as Halle Berry, her face
picture, her name, and
pictures of her dressed
as Catwoman from
Batman.
But the hippocampus is
a memory storage site.
So, these specific
neurons are responding
to specific memory of a
familiar person.
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Distributed coding
The same set of neurons
respond to different faces but
in different degrees.
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Combinations of neurons can
express lots of different faces
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