GENERAL PSYCHOLOGY
Lecture 4
Brain,Sensation,Perception
Visiting Assistant PROFESSOR YEE-SAN TEOH
Department of Psychology
National Taiwan University
Unless noted, the course materials are licensed
under Creative Commons AttributionNonCommercial-ShareAlike 3.0 Taiwan
(CC BY-NC-SA 3.0)
The Brain and the Nervous System
THE NERVOUS SYSTEM
METHODS FOR STUDYING THE NERVOUS
SYSTEM
RESULTS OF CORTICAL DAMAGE
BRAIN PLASTICITY
Building Blocks of the Nervous System - Neurons
 Communicates with each other by releasing
neurotransmitters, special chemicals that move through the
synapses.
Brain Development in Infancy
 After birth, a baby’s brain increases in size because
existing neurons grow, and connections between
them proliferate.
 Connections between neurons are formed via
synaptogenesis.
 Brain is programmed to create more neurons &
connections than are needed.
 2 developmental processes reduce the number of
neurons & synapses (Sowell et al., 2003)
(i)Neuronal death
(ii)Synaptic pruning
 Goal of reduction of neurons & synapses :
(a)Increase speed, efficiency, & complexity of
transmissions between neurons,
(b)Accommodate new connections that develop with
increasing experience with the world. (Kolb et al, 2003)
Neurotransmitters
 Large number of neurotransmitters allows the
specialization of information sent throughout the
brain.
a. Individual neurons are selective in what
neurotransmitters they will respond to.
b. Each neuron has its own pattern of sensitivities to
the neurotransmitters.
 Neurotransmitters are received by receptors, sites on
the postsynaptic neuron shaped to fit specific
neurotransmitters.
Lock & Key model:
Neurotransmitter molecules will affect the
postsynaptic membrane only if the molecule’s
shape fits perfectly into the receptor.
Drugs & Neurotransmitters
 Drugs can enhance or impede the actions of a
neurotransmitter.
a) Agonists: chemicals (drugs) that enhance a
neurotransmitter’s activity.
b) Antagonists: chemicals that impede a
neurotransmitter’s activity.
Methods for Studying the
Nervous System
RECORDING FROM INDIVIDUAL NEURONS
STUDYING THE EFFECTS OF BRAIN DAMAGE
RECORDING FROM THE WHOLE BRAIN
COMBINATION OF TECHNIQUES
Recording from Individual Neurons
1.
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2.
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Single-cell recordings
Monitor moment-by-moment activity of the individual
neurons in the brain while stimuli is presented to subject.
Identifies apparent function of each neuron.
Multiunit recordings
Use computer analyses to examine patterns of activity
across the entire collection of cells.
Understand how each cell influences others, overall
response.
Studying the Effects of Brain Damage
Previous ‘popular’ methods, but unethical
Brain Lesions
-Create damage to brain cells at a particular site
-Compare how the brain functions before and after this
damage.
Transecting
-Surgical cutting of a nerve tract or brain region performed
to isolate functionally the regions on either side.
-Transect the relevant pathways & observe the result.
Neuropsychological Studies
 Examine brain-behavior relationships using evidence
from cases of brain damage.
 Close observation of changes in function associated
with brain damage.
 Conduct experiments to determine what a braindamaged individual can and cannot do.
 Use neuroimaging techniques.
The Story of Phineas Gage
Impaled by iron rod – profound
damage to left frontal lobe.
Physical health almost fully recovered,
except for left eye.
No problems with speech or other
abilities.
Severe personality change, almost to a
different person (from nice to mean).
Inability to execute plans.
NEUROIMAGING
TECHNIQUES
CT/CAT SCAN
 Computerized tomography scan.
 Use computer to construct a detailed composite
portrait of the brain.
 X-ray pictures taken from different angles.
 Useful for medical diagnosis – detecting tumors.
MRI/fMRI SCANS
 MRI - magnetic resonance imaging
- Uses nuclear magnetic resonance to provide a more precise
portrait of the brain compared with CT.
- Passes a high-frequency, alternating magnetic field through
the brain.
- Computer forms a picture of brain structure that shows
healthy tissues, as well as tumors, tissue degeneration, bloody
clots or leaks.
 fMRI – functional MRI
- Measures fast-changing physiology (bloodflow & oxygen use)
- In addition to picture of brain, allows examination of brain
functioning.
PET SCAN
 Positron Emission Tomography
 Does not give clear picture of
brain
 Person is injected with a safe dose
of some radioisotope, which will
be absorbed by certain active
brain cells.
 By observing metabolic activity,
one can see on the scan which
regions are active.
Recording the Brain’s Electrical Activity
1.
-
2.
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EEG (Electroencephalogram)
Records summed activity of the cortical cells detected by
wires placed on the skull.
Records detectable rhythm in brain’s electrical activity.
ERP (Event-related potentials)
Records changes in the EEG just before, during, and after
a specific event.
Has to be repeated to average the results in order to
cancel out background activities and isolate signals.
Transcranial Magnetic Stimulation Studies
 Production of temporary brain disruption.
 Repeated magnetic stimulation at the surface of the
skull is used to stimulate or cause a temporary lesion
of a region of the brain.
 Effects of stimulation/lesion can be recorded.
 Can only study structures immediately below the
skull.
Brain Hemispheric
Specialization
LATERALIZATION
Hemispheric Specialization (HS)
 Begins early in life (Stephan et al., 2003).
 Lateralization = specialization of each hemisphere
in specific perceptual & cognitive tasks.
 Genetic basis – e.g. similar language lateralization
between parents & children (Anneken et al., 2004).
Hemispheric Specialization (HS)
 Brain can adapt to external change (e.g. brain
damage)
– In deaf persons who use sign language (that involves
motor area), right brain takes over language
functions (Sanders et al., 2007).
Consequences of Brain Lateralization
 Dyslexia…
- Difficulty learning to read : Integrating visual & auditory
information.
- E.g. matching written letters/words to sounds of those
letters/words. (confusing d and b)
- Abnormal lateralization pattern – process spatial info on
both hemispheres, rather than primarily on the right
(Baringa, 1996; Veuillet et al., 2007).
 Handedness…
- Genetic basis (Francks, 2007)
- Left-handed people can be ambidexterous - brains may
be less clearly lateralized than brains of right-handed
people.
Results of Cortical Damage
Disorders of Action
 Apraxias – serious disturbances in the initiation or
organization of voluntary action.
 Damage to the frontal lobes.
 Inability to perform well-known actions such as
waving goodbye.
 Disconnection between preparation for action and
production of action.
Disorders of Perception & Attention
 Disruption in the way a person perceives the world
(e.g. motion, color)
 Visual agnosia – inability to recognize object
although it can be seen.
 Prosopagnosia – inability to recognize faces.
 Neglect syndrome – problem of attention.
Disorders of Language
 Aphasias – disruptions in the production or
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comprehension of speech.
Almost always produced by damage to the left
hemisphere.
Mute silence, broken speech
(“Here…head…operation….here…speech”)
Able to produce speech, but unable to understand
what is said to them.
Nonsense speech.
Disorders of Planning
 Damage to the prefrontal area.
 Disruption to person’s executive control over his/her
thinking and planning.
 Inability to make plans, strategize, set priorities.
 Perseveration – unable to switch tactics, tendency to
repeat the same response or strategy repeatedly even
after feedback.
Brain Injury in Early Years of Life
 Young brain is not fully developed, hemispheric
specialization not fully complete…
 Infants & young children often recover their
functioning (Stiles, 2000).
 Example: despite left hemisphere damage in early
infancy , child can still develop language normally
(Bates & Roe, 2001).
Brain Damage due to
Negative/Lack of Experiences
 Lack of stimulation or exposure to traumatic events
can damage the brain and cause it to malfunction.
 In abused children, the cortex and limbic system that
are involved with emotions and parent-child
attachment – are 20%-30% smaller, have fewer
synapses.
 Recovery or improvement depends on other
environmental factors, removal from negative
environment, and genotype.
Brain Plasticity
• The capacity of the brain to
respond and adapt to input from
the external environment.
2 types of experience influence brain
development (Greenough & Black, 1999):
1.Experience-expectant processes = experiences that are
expected in all environments (e.g. touch, patterned visual input,
sounds of language, social interaction, nutrition)
2.Experience-dependent processes = experiences unique to
individuals, encountered in particular families, communities,
cultures.
Infants’ Brain Plasticity: Native Language
 Newborns respond to sounds of all languages.
 Over 1st year of life – more selective responses, show
bias towards sounds they hear in their own language
(Kuhl, 2004).
 Brains develops auditory ‘maps’ that respond to
certain sounds and not others – guide infants in
recognizing native language.
Sensation & Perception
Sensory Thresholds
 Our sensory detection can be defined in terms of
stimulus intensities…
1. Absolute threshold – smallest quantity of an
input that can be detected.
2.Difference threshold – smallest change in an
input that can be detected; amount by which a given
stimulus must be increased or decreased so that a
person can just perceive a just-noticeable difference
(Jnd)
Sensory Thresholds
 Just-noticeable Difference - The smallest possible

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difference between two stimuli that an organism can
reliably detect.
Weber’s Law
Size of the difference threshold is proportional to the
intensity of the standard stimulus.
The smaller the fraction, the more sensitive the sense
modality
E.g. Eyes are more sensitive to detecting differences in
brightness (1.6% difference needed to detect a change)
than our ears in detecting difference in loudness (10%)
Sensory Detection & Decision
Signal Detection Theory
The act of perceiving or not perceiving a stimulus is
actually a judgment about whether a momentary
sensory experience is due to background noise alone
or to a background noise plus a signal.
We are not just passive information receivers
Sensory Detection & Decision
Signal Detection Procedure
Experimenter presents a faint target stimulus on
some trials, but not stimulus on other trials.
Asks each participant to respond by saying “Yes, I
detected the target” or “No target”.
There are 4 possible responses: Hit, False Alarm,
Correct Negative/Rejection, Miss.
Studying Sensory Detection
 By examining participants’ rates of responding in
each category, we can see differences in their
(a) Perceptual sensitivity
(b) Decision criteria
Our Senses – Sensory
Processing
Sensory Information is
subjected to
Sensory Coding
Sensory Adaptation
Sensory Coding
 Qualities of the sensory input are translated into
specific representations within the nervous system.
 Example: Did we see or hear a cat, or was the cat
black or brown?
 Sensory coding is applied to
i. Psychological Intensity
ii. Sensory Quality
Sensory Coding
Psychological Intensity
 Magnitude of the stimulus as it is perceived.
 The more intense the stimulus, the more neuron it
activates, and the greater the firing by the neurons.
 E.g. bright light vs dim light; strong scent vs subtle
scent.
Sensory Coding
Sensory Quality
 Distinguishing quality of the physical stimulus.
 E.g. brightness, hue, pitch
 Differences between sensory modalities (seeing or
hearing) are signaled by the stimulation of different
nerves.
 Differences within sensory modalities are signaled by
stimulation of the sensory neurons.
 Individual sensory neurons may ‘specialize’ in
specific qualities, or neurons may have a specific
firing pattern.
Sensory Adaptation
 Process by which the sensitivity to a stimulus
declines if the stimulus is continually presented.
 Our sensory neurons will respond strongly to a
stimulus when it first arrives, but if the stimulus is
unchanging, our sensory response gradually
decreases.
 E.g. coldness of water when you first jump into the
pool decreases as you remain in the pool.
 Sensory adaptation of vision will occur only under
certain conditions, e.g. when the we hold our eyes
very still.
Various Senses
SOMESTHETIC SENSES
SMELL
TASTE
HEARING
VISION
Somesthetic Senses
Somesthetic Senses
Kinesthesis
• Sensations coming from muscles,
tendons, joints.
• Sense of movement, space orientation.
Vestibular
Sense
• Movements of the head.
• Provides firm basis for vision.
Skin Senses
• Pressure, Temperature
• Pain – modulated by e.g. endorphins
Smell
Smell
 We have about 1,000 receptor types in the nose.
 We can distinguish roughly 10,000 different odors.
 Each odor gives rise to some unique pattern of
activation, not individual receptor.
 Used for recognition (identification of species),
communication (where they are, what condition they
are in, alarm signals), mating (role in humans is
inconclusive).
Taste
Taste
 Number of receptors change with age.
 Each taste receptor responds to all the tastants, but they
prefer one taste over the rest.
 Taste preferences may be evolutionary – preference for
sweets and avoidance of bitter tastes (nutrition vs toxins).
 Supertasters are enormously sensitive to certain tastes.
 Taste can be influenced by learning.
Hearing
Hearing
 Neurons carry auditory signals to the primary
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auditory projection area.
Signals are analyzed for the purity of sound.
Signal must be tracked across time to evaluate pitch
change, e.g. distinguish a question from a command.
Neurons along auditory pathway respond to various
pitches but each have a preferred pitch.
We must look at the overall pattern of firing of the
neurons to detect pitch.
Vision
Color Perception
 Light emitted and reflected by many objects enables
us to see.
 Photoreceptors – one of the visual-pigment-filled
light-sensitive cells at the back of the retina transduce light energy into neural impulses
 2 Types of Photoreceptors:
i. Cones – respond to greater light intensities,
give rise to chromatic (color) sensations.
ii. Rods – respond to lower light intensities,
give rise to achromatic (colorless) sensations.
Color Blindness
 Types: Most common is confusion between red and
green; least common is total color blindness.
 Can be due to:
(i)Missing one of the three visual photopigments
(ii)Malfunction in brain circuitry needed for
color vision.
 Most commonly has a genetic origin, much more
common in men.
Object Recognition
 Our primary means of recognizing objects is
through the perception of their form, although we
also rely on color and size…
 But how?
Organization of Our Perception of Visual Stimuli
Features
Interpretation
Organization
We choose which
features are
important for our
recognition of the
object and which
are not as
important.
Features present
in the object
depends on how
we interpret its
overall form.
With our
interpretation of
the object, we
organize the
overall form by
filling in missing
pieces.
Perceptual Parsing
 Gestalt Psychology – organization is an essential feature
of all mental activity; emphasizes the role of organized
wholes in perception.
 Parsing – separate a scene into individual objects, linking
together the parts of each object that go together.
 Principles of Parsing:
i. Similarity – group figures that resemble each other
ii. Proximity – group figures that are closer to each other
iii. Good continuation – contours continue smoothly
iv. Subjective contours – perceive contour to complete
picture
Figure & Ground
 Separation of the visual field into a part (the figure)
that stands out against the rest (the ground).
 Allows one to focus on the figure.
 Usually the figure is perceived as being closer to the
viewer than the background.
 Visual organization of a figure-ground stimulus up to
the perceiver.
Network Models of Perception
 Evidence from visual search task supports the
importance of features.
Visual search task
- Subject is asked to locate a specified target within a
field of stimuli.
- Identity of the target can be defined in various ways
(“look for the green item”)
- Background items can vary both in number and
identity.
- No need to scan each item, just look at the display as
a whole.
Feature Nets
 Perception occurs through the activation of a
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hierarchy of detectors.
Detectors in each layer serve as the triggers for
detectors in the next layer.
Lowest level - feature detectors (respond to
horizontals, verticals, etc)
Higher levels - detectors that respond to the
combinations of simple features.
Activation of the feature nets can flow from bottomup and top-down simultaneously.
Parallel Processing in the Visual Cortex
 Different cells & different areas of the brain specialize
in a particular kind of analysis of a stimulus.
 These different analyses occur in parallel.
 Some cells are analyzing form, while others are
analyzing motion, others are analyzing color, and so
on.
 Parallel processing promotes efficiency, interaction
between systems.
Perceptual Constancy
 Despite differences due to proximity, we are still able
to perceive attributes of an object as being constantshape, size, brightness.
 Objects retain their size, shape & brightness despite
the change in viewing distance, angle, and
illumination.
Visual Illusions
 Normal mechanisms of perceptual
constancy involve making adjustments for
details, like viewing angles, contrast effects,
etc.
 These adjustments can cause
misperceptions of depth or brightness,
resulting in illusions.