Download PY460: Physiological Psychology

Chapter Six: Vision
Assorted Materials from Modules 1-3
Chapter Seven: Audition
Module 1
Visual Coding and Retinal Receptors
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Reception- absorption of physical energy
(electromagnetic waves) by receptors
Transduction-the conversion of physical energy
to an electrochemical pattern in the neurons
Coding- one-to-one correspondence between
some aspect of the physical stimulus and some
aspect of the nervous system activity
Visual Coding and Retinal Receptors
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From Neuronal Activity to Perception
 coding of visual information in the brain does not duplicate the
stimulus being viewed
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General Principles of Sensory Coding
 Muller and the law of specific energies-any activity by a particular
nerve always conveys the same kind of information to the brain
 Now close your lid and poke your eye… do you see light
(fosphenes)(sp?)
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Qualifications of the Law of Specific Energies
 the rate of firing or pattern of firing may signal independent stimuli
 timing of action potentials may signal important information
indicating such things as movement
 the meaning of one neuron depends on what other neurons are
active at the same time
Visual Coding and Retinal Receptors“Look into My Eyes!”
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The Eye and Its Connections to the Brain
Pupil-opening in the center of the eye that allows
light to pass through
Lens-focuses the light on the retina
Retina-back surface of the eye that contains the
photoreceptors
The Fovea-point of central focus on the retina
The Route Within the Retina
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photoreceptors-rods and cones
bipolar cells-receive input from rods and cones
ganglion cells-receive input from bipolar cells
optic nerve-made up of axons of ganglion cells
blind spot-the point where the optic nerve leaves the eye
Figure 6.2 Cross section of the vertebrate eye
Note how an object in the visual field produces an inverted image on the retina.
Figure 6.4 Visual path
within the eyeball
The receptors send their
messages to bipolar and
horizontal cells, which in turn
send messages to the
amacrine and ganglion cells.
The axons of the ganglion
cells loop together to exit the
eye at the blind spot. They
form the optic nerve, which
continues to the brain.
Receptive Field- the part of the
visual field to which any one
neuron responds
Key Point: Fields have both
excitatory and inhibitory regions
•The receptive field of a
receptor is simply the area of
the visual field from which light
strikes that receptor.
•The receptive field for any
other neurons in the visual
system is determined by which
receptors connect to the cell in
question.
Figure 6.6 Two
demonstrations of
the blind spot of the
retina
Close your left eye and
focus your right eye on
the o in the top part.
Move the page toward
you and away, noticing
what happens to the x.
At a distance of about
25 cm (10 inches), the
x disappears. Now
repeat this procedure
with the bottom part. At
that same distance
what do you see?
Visual Receptors: Rods and Cones,
Reception & Transduction continued
Rods
-abundant in the periphery
of the retina
-best for low light
conditions
-see black/white and shades
of gray
Cones
abundant around fovea
best for bright light
conditions
see color
Table 6.1 is very good
Transduction
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Both Rods and Cones contain photopigments
(chemicals that release energy when struck by light)
 11-cis-retinal is transformed into all-trans-retinal in light
conditions
 this results in hyperpolarization of the photoreceptor
 the normal message from the photoreceptor is inhibitory
 Light inhibits the inhibitory photoreceptors and results in
depolarization of bipolar and ganglion cells
Theories Color Vision
The Trichromatic (Young-Helmholtz) Theory
KEY POINT: We perceive color through
the relative rates of response by three
kind of cones, each kind maximally
sensitive to a different set of wavelengths,
but receptors are not equally distributed
across retina. (exercises)
Bowmaker & Dartnall (1980) projected a
known amount of light directly through
the outer segments of photoreceptors
and measured how much light was
absorbed by the photopigment
molecules.
They found four classes of photopigments. The wavelength of maximum absorbance is indicated
at the top of each curve. The 420 curve is for the short wavelength cones (blue), the 498 curve is
for the rods, and the 534 and 564 curves are for the middle (green) and long wavelength (red)
sensitive cones respectively.
More Theories of Color Vision
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The Opponent-Process Theory
 we perceive color in terms of paired opposites
 RED vs. GREEN; YELLOW vs. BLUE; BLACK vs. WHITE
 one color the result of excitation, the other the result of inhibition
of bipolar cells
Can explain negative color after-image effects
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The Retinex Theory
 When information from various parts of the retina reaches the
cortex, the cortex compares each of the inputs to determine the
brightness and color perception for each area.
 can explain color constancy
 only works when entire view has been tinted
Figure 6.12 Possible wiring for one
bipolar cell
Short-wavelength light (which we see as
blue) excites the bipolar cell and (by way
of the intermediate horizontal cell) also
inhibits it. However, the excitation
predominates, so blue light produces net
excitation. Red, green, or yellow light
inhibit this bipolar cell because they
produce inhibition (through the horizontal
cell) without any excitation. The
strongest inhibition is from yellow light,
which stimulates both the long- and
medium-wavelength cones. Therefore
we can describe this bipolar cell as
excited by blue and inhibited by yellow.
White light produces as much inhibition
as excitation and therefore no net effect.
(Actually, receptors excite by decreasing
their usual inhibitory messages. Here we
translate that double negative into
excitation for simplicity.)
Neural Basis of Visual Perception
An Overview of the Mammalian Visual System
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Rods and Cones synapse to
amacrine cells and bipolar
cells
Bipolar cells synapse to
horizontal cells and
ganglion cells
Axons of the ganglion cells
leave the back of the eye
The inside half of the axons
of each eye cross over in
the optic chiasm
Pass through the lateral
geniculate nucleus
Transferred to visual areas
of cerebral cortex
Neural Basis of Visual Perception
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Concurrent Pathways in the Visual System
 In the Retina and Lateral Geniculate
 Two categories of Ganglion cells
– Parvocellular-smaller cell bodies and small receptive
fields, located near fovea; detect visual details, color
– Magnocellular-larger cell bodies and receptive fields,
distributed fairly evenly throughout retina; respond to
moving stimuli and patterns
 In the Cerebral Cortex
 V1-Primary Visual Cortex-responsible for first stage visual
processing
 V2-Secondary Visual Cortex-conducts a second stage of
visual processing and transmits the information to additional
areas
 Ventral stream-visual paths in the temporal cortex
 Dorsal stream-visual path in the parietal cortex
Figure 6.20 Three visual
pathways in the cerebral
cortex
(a) A pathway originating
mainly from magnocellular
neurons. (b) A mixed
magnocellular/parvocellular
pathway. (c) A mainly
parvocellular pathway. Neurons
are heavily connected with
other neurons in their own
pathway but only sparsely
connected with neurons of
other pathways. Area V1 gets
its primary input from the lateral
geniculate nucleus of the
thalamus; the other areas get
some input from the thalamus
but most from cortical areas.
(Sources: Based on DeYoe,
Felleman, Van Essen, &
McClendon, 1994; Ts’o & Roe,
1995; Van Essen & DeYoe,
1995)
Neural Basis of Visual Perception-
The Cerebral Cortex: The Shape Pathway
Hubel and Wiesel’s Cell Types in the
Primary Visual Cortex
Simple Cells
has fixed excitatory and inhibitory zones in
its receptive field
Complex
Cells
receptive fields cannot be mapped into fixed
excitatory and inhibitory zones
Respond to a pattern of light in a particular
orientation
Figure: The receptive field of a complex cell in the
visual cortex:
-It is like a simple cell in that its response depends on
a bar of light’s angle of orientation.
-It is unlike a simple cell in that its response is the
same for a bar in any position within the receptive
field.
Neural Basis of Visual Perception-
The Columnar Organization of the Visual Cortex
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Columns are grouped together by function
– Ex: cell within a given column respond best to lines of
a single orientation
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Are Visual Cortex Cells Feature Detectors?
 Feature Detectors-neurons whose responses indicate the
presence of a particular feature
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Shape Analysis Beyond Areas V1 and V2
 Inferior Temporal Cortex (V3)-detailed information about
stimulus shape
 (V4)-Color Constancy; Visual Attention
 (V5)-Speed and Direction of Movement
Neural Basis of Perceptual Disorder
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Disorders of Object Recognition
 Visual Agnosia-Inability to Recognize Objects
 Prosopagnosia-Inability to recognize faces
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Color Vision Deficiencies
 Complete and Partial Color Blindness-inability to perceive
color differences
 Generally results from people lacking different subsets of
cones
 genetic contributions- same photopigment made on
medium and longwave wavelength receptors
Neural Basis of Visual PerceptionThe Cerebral Cortex
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The Cerebral Cortex: The Color Pathway
 Parvocellular to V1 (blobs) to V2, V4, and Posterior Inferior
Temporal Cortex
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The Cerebral Cortex: The Motion and Depth Pathways
 Structures Important for Motion Perception
 Middle-temporal cortex-V5-speed and direction of
movement
 Motion Blindness-Inability to detect objects are moving
Experience and Visual Development
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Early Lack of Stimulation of One Eye-blindness occurs in that one
eye
Early Lack of Stimulation of Both Eyes-if this occurs over a long
period of time, loss of sharp receptive fields is noted
Restoration of Response and Early Deprivation of Vision-deprive
stimulation of the previously active eye and new connections will
be made with the inactive eye
Uncorrelated Stimulation in Both Eyes-each cortical neuron
becomes responsive to the axons from just one eye and not the
other
Experience and Visual Development
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Early Exposure to a Limited Array of Patterns—most of
the neurons in the cortex become responsive only to the
patterns that the subject has been exposed to
Lack of Seeing Objects in Motion-become permanently
disable at perceiving motion
Effects of Blindness on the Cortex-parts of the visual
cortex become more responsive to auditory and tactile
stimulation
Chapter Seven
The Nonvisual Sensory Systems- Auditory System
Module One
Audition
Sound and the Ear
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Physical and
Psychological
Dimensions of Sound
 Amplitude=intensity of
wave=loudness
 frequency=number of
waves/second=pitch
Figure 7.1 Four sound waves
The time between the peaks determines the frequency of the sound, which we experience
as pitch. Here the top line represents five sound waves in 0.1 second, or 50 Hz—a very
low-frequency sound that we experience as a very low pitch. The other three lines represent
100 Hz. The vertical extent of each line represents its amplitude or intensity, which we
experience as loudness.
Anatomy of the Ear
Structures of the Ear
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Pinna-cartilage attached to the
side of the head
Tympanic Membrane-eardrum
middle ear boneshammer/anvil/stirrup
oval window-membrane leading to
inner ear
cochlea-three fluid-filled tunnels
 scala vestibuli
 scala media
 scala tympani
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basilar membrane-flexible
membrane
tectorial membrane-rigid
membrane
hair cells-auditory receptors
Figure 7.2 Structures of the ear
When sound waves strike the tympanic membrane in (a), they cause it to
vibrate three tiny bones—the hammer, anvil, and stirrup—that convert the
sound waves into stronger vibrations in the fluid-filled cochlea (b). Those
vibrations displace the hair cells along the basilar membrane in the cochlea.
(c) A cross section through the cochlea. The array of hair cells in the
cochlea is known as the organ of Corti. (d) A closeup of the hair cells.
Pitch Perception
Theories of Pitch Perception
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Frequency theory the basilar membrane vibrates in synchrony with a sound,
causing auditory nerve axons to produce action potentials at
the same frequency
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Place theory the basilar membrane resembles the strings of a piano in that
each area along the membrane is tuned to a specific frequency
and vibrates whenever that frequency is present
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Volley principle the auditory nerve as a whole can have volleys of impulses up
to about 5,000 per second, even though no individual axon can
approach that frequency by itself
Figure 7.4 The basilar
membrane of the
human cochlea
High-frequency sounds
produce their maximum
displacement near the
base. Low-frequency
sounds produce their
maximum displacement
near the apex.
Figure 7.5 Traveling waves in the
basilar membrane set up by different
frequencies of sound
Note that the peak displacement is
closer to the base of the cochlea for high
frequencies and is toward the apex for
lower frequencies. In reality the peak of
each wave is much narrower than shown
here.
Pitch Perception in the Cerebral Cortex
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Primary auditory cortex
Each cell responds best to one tone
Cells preferring a given tone cluster together
Secondary auditory cortex
Each cell responds to a complex combination of sounds
Figure 7.6 Route of auditory impulses from the receptors
in the ear to the auditory cortex
The cochlear nucleus receives input from the ipsilateral ear only (the one on the same
side of the head). All later stages have input originating from both ears.
Hearing Loss
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Conductive Deafness
 bones of the middle ear fail
 caused by tumors, infection, disease
 usually corrected by surgery or hearing aids
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Nerve Deafness
 damage to cochlea, hair cells or auditory nerve
 usually treated with hearing aids
 caused by genetics, disease, ototoxic drugs, etc.
Localization of Sound
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Sound Shadowloudest in
nearest ear
Time of arrivalarrives at one ear
soonest
Phase differencesounds arrive out
of phase
dependent on
frequency
Figure 7.10 Phase differences between the ears as a cue for sound localization
Note that a low-frequency tone (a) arrives at the ears slightly out of phase. The ear for which the
receptors fire first (here the person’s left ear) is interpreted as being closer to the sound. If the
difference in phase between the ears is small, then the sound source is close to the center of the body.
However, with a high-frequency sound (b) the phase differences become ambiguous. The person
cannot tell which sound wave in the left ear corresponds to which sound wave in the right ear.