James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
1 of 48
Chapter Six
Vision
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
2 of 48
General Principles of Perception
•
•
Water strikes iron and iron experiences rust, not water
Light from a tree leaf strikes your eye and you experience
green, not colorless light
– visual receptors are specialized to absorb light and
transduce it into an electrochemical pattern in the brain
– not a duplicate, picture-like pattern of the object
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Law of Specific Nerve Energies
•
•
Müller (1838): the neuron action potential always conveys the
same kind of information
– brain “sees” the activity of optic neurons and “hears” the
activity of the auditory neurons
Von Melchner, Pallas & Sur (2000)
– routed the optic nerve on left side of ferret’s immature
brain to the auditory area of the thalamus
– the adult ferret “saw” activity of optic nerve in the
thalamus and cortex normally used for auditory input
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Figure 6.1
Figure 6.1 Behavior of a ferret with a rewired temporal cortex. First the normal (right) hemisphere is
trained to respond to a red light by turning to the right. Then the rewired (left) hemisphere is tested with a
red light. The fact that the ferret turns to the right indicates that it regards the stimulus as light, not sound.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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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 is lined by visual
receptors
– light from above strikes bottom and light from below
strikes top
– light from left strikes right side and vice versa
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
6 of 48
Figure 6.2
Figure 6.2 Cross section of the vertebrate eye. Note how an object in the visual field produces an
inverted image on the retina.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Route Within the Retina
•
•
Light passes through ganglion and bipolar cells, without
distortion, to visual receptors
– bipolar cells receive input from visual receptors
– ganglion cells receive input from bipolar cells
– amacrine cells exchange information with bipolar cells
and send information to ganglion and other amacrine cells
• provides many options for complex processing of
information
Optic nerve is made up of axons of ganglion cells
– the point where optic nerve leaves the eye does not have
receptors and is our blind spot
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Figure 6.3
Figure 6.3 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.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Fovea and Periphery of Retina
•
•
Macula: 3mm X 5mm center of retina with greatest ability to
resolve detail
– fovea, the center of the macula, provides most detail
– each visual receptor has direct pathway to the brain
through to one bipolar cell and one midget ganglion cell
• provides exact location of a point of light
Periphery of retina provides better sensitivity to dim light
– multiple receptors converge onto bipolar and ganglion
cells
– can’t detect exact location or shape of light but
convergence enables detection of very faint light
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Figure 6.5
Figure 6.5 Types of cells in the vertebrate retina. Note the huge variation among amacrine cells, which
have diverse functions. Note also the variation among ganglion cells. Those in and near the fovea have a
narrow span of dendrites and receive input from few receptors. Those in the periphery integrate input from
a wide field of receptors. (Source: Masland, 2000.)
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Fovea and Periphery of Retina cont.
•
•
Many bird species have two foveas per eye
– one pointing ahead and one pointing to the side
Visual receptors in some predators and prey are designed to
facilitate survival
– hawks have greater density on top half (looking down)
than on the bottom half (looking up)
– rats have greater density on the bottom half (looking up)
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
12 of 48
Rods and Cones
•
•
Rods: visual receptors that are abundant in the periphery of
the retina
– respond best to low light conditions
– bleached by bright light
Cones: visual receptors that are abundant in and around the
fovea
– respond best to bright light conditions
– essential for color vision
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Rods and Cones cont.
•
•
•
•
100 million cones and 6 million rods
But rods send 10 times more responses to brain than cones
Each cone has direct line to brain while many rods share
same line
Both rods and cones contain photopigments, chemicals that
release energy when struck by light
– light is absorbed and 11-cis-retinal is converted to alltrans-retinal
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color Vision
•
The trichromatic, or Young-Helmholtz, theory
– we can perceive color only within the visible wavelengths
of light, ranging from 400-700 nm (violet to red)
– we see a specific color by comparing responses from 3
kinds of cones, each most sensitive to a short, medium,
or long wavelength of light
• Ex: blue-green excites short wavelength to 15% of
maximum, medium to 65% and long to 40%
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color Vision cont.
•
The trichromatic, or Young-Helmholtz, theory cont,
– fewer short wavelength cones (blue) so we see red,
yellow, and green colors better
– when all 3 cones are equally active we see white or gray
– Incomplete theory, e.g., can’t explain negative color
afterimage
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Figure 6.9
Figure 6.9 A beam of light separated into wavelengths. Although the wavelengths vary over a
continuum, we perceive them as several distinct colors.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color Vision cont.
•
The opponent-process theory
– brain sees color on a continuum from red to green and
another from yellow to blue
– we perceive color in terms of “paired opposites” redgreen, black-white and yellow-blue
• explains why we can’t see reddish green or bluish
yellow
• explains negative color afterimages
– not a complete explanation since afterimages depend not
only on the retina but also on the area of the brain that
produces it
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Figure 6.13
Figure 6.13 Possible wiring for one bipolar cell. Short-wavelength light produces more excitation than
inhibition and the result is seen as blue. Other wavelengths produce mostly inhibition, perceived as yellow.
White light produces about equal excitation and inhibition.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color Vision cont.
•
The retinex theory
– color perception requires some reasoning
– the cortex compares information from various areas of the
retina to determine the brightness and color perception for
each area
• color constancy: we see the right colors despite
lighting changes, e.g., we subtract green tint to see
white house and red rose but we only see green
house if viewed in isolation
• brightness requires a comparison with other objects
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color Vision Deficiency
•
Inability to perceive color differences
– genetic: lack of short- medium- or long-wavelength cones
• some people lack two types of cones
• some people have low number of all three
– inability to distinguish red from green is most common
deficiency
• recessive gene on X chromosome
• 8% in men and 1% in women
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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The Mammalian Visual System
•
Within the eyeball
– rods and cones synapse to horizontal cells and bipolar
cells
– horizontal cells make inhibitory synapse onto bipolar cells
– bipolar cells synapse to amacrine and ganglion cells
– axons of the ganglion cells leave the back of the eye
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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The Mammalian Visual System cont.
•
The inside half of the axons of each eye cross over in the
optic chiasm
– most visual information goes through the lateral
geniculate nucleus of the thalamus
– some goes to the superior colliculus
– lateral geniculate inputs to other parts of thalamus and to
visual areas of cerebral cortex, which sends back axons
to modify input
• number of neurons within this loop varies widely
among people by a factor of 2 or 3
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
23 of 48
Figure 6.17
Figure 6.17 Major connections in the visual system of the brain. Part of the visual input goes to the
thalamus and from there to the visual cortex. Another part of the visual input goes to the superior colliculus.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
24 of 48
Mechanisms of Processing in the Visual System
•
Receptive field: the point in space from which incoming light
strikes a receptor
– receptors have both excitatory and inhibitory regions
since receptive field is normally an array of light patterns
• Ex: light in center of ganglion cell might be excitatory,
with the surround inhibitory
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
25 of 48
Figure 6.18
Figure 6.18 Receptive fields. The receptive field of a receptor is simply the area of the visual field that
strikes that receptor. For any other cell in the visual system, the receptive field is the collective receptors
feeding the neural pathway to the cell.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
26 of 48
Mechanisms of Processing in the Visual System cont.
•
Lateral Inhibition: each active receptor and it’s visual path
tends to inhibit the visual path of neighboring receptors
– an active receptor excites both a bipolar and horizontal
cell; in turn, horizontal cell inhibits bipolar cell, but net
potential is excitatory on bipolar
– but, horizontal cell does inhibit neighboring bipolar cells
on border of visual field
– effect is to heighten contrast: receptors inside visual field
are excited and those on border tend to be inhibited
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
27 of 48
Figure 6.20
Figure 6.20 An illustration of lateral inhibition. Do you see dark diamonds at the “crossroads” due to
inhibition from all four corners of intersection?
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
28 of 48
Retina and Lateral Geniculate Pathways
•
•
Parvocellular: smaller ganglion cell bodies and small
receptive fields, located near fovea
– detect visual detail and color
– all axons go to lateral geniculate nucleus
Magnocellular: larger ganglion cell bodies and receptive
fields, distributed fairly evenly throughout retina
– respond to moving stimuli and patterns
– not color sensitive
– most axons go to lateral geniculate nucleus
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
29 of 48
Retina and Lateral Geniculate Pathways cont.
•
•
Koniocellular: small ganglion cell bodies that occur
throughout the retina
– many functions
– axons go to lateral geniculate nucleus, thalamus and
superior colliculus
Many different types of ganglion cells implies analysis of
information from the beginning
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Pathways in Cerebral Cortex
•
•
•
Most visual information from lateral geniculate nucleus goes
to primary visual cortex (V1)
– first stage of visual processing
Output of V1 goes to secondary visual cortex (V2)
– second stage of visual processing which transmits visual
information to additional areas
– feedback loop to V1
– V1 and V2 also exchange information with other cortical
areas and thalamus
30-40 visual areas reported in brain of macaque monkey
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Pathways in Cerebral Cortex cont.
•
Magnocellular and parvocellular paths split into three paths
– Magnocellular path
• ventral branch to temporal cortex is sensitive to
movement
• dorsal branch to parietal cortex integrates vision with
action
– Parvocellular path to temporal cortex is sensitive to details
of shape
– Mixed parvo/magnocellular path to temporal cortex is
sensitive to brightness and color
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
32 of 48
Figure 6.21
Figure 6.21 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 only sparsely connected with neurons of other pathways. (Sources: Based on
DeYoe, Felleman, Van Essen, & McClendon, 1994; Ts’o & Roe, 1995; Van Essen & DeYoe, 1995.)
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Pathways in Cerebral Cortex cont.
•
•
Visual paths in temporal cortex form the ventral stream
– the “what” path, specialized for identifying and
recognizing objects
– if damaged, we can find and pick up objects but cannot
describe them
Visual path in parietal cortex is the dorsal stream
– the “where” or “how” path, helps motor system find
objects, move toward them and pick them up
– if damaged, we can describe object but can’t find and pick
up object
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
34 of 48
The Shape Pathway in the Cerebral Cortex
•
•
•
Simple cells (fixed, small receptive field)
– have fixed excitatory and inhibitory zones
– most have bar- or edge-shaped receptive fields
Complex cells (large receptive field)
– respond to a particular orientation anywhere within large
receptive field
– receive input from combination of simple cells
End-stopped or hypercomplex cells
– resemble complex cells with a strong inhibitory area at
one end of its bar-shaped receptive field
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
35 of 48
Figure 6.24
Figure 6.24 The receptive field of a complex cell in the visual cortex. Like a simple cell’s, its response
depends on the angle of orientation of a bar of light. However, a complex cell responds the same for a bar
in any position within the receptive field.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
36 of 48
Shape Pathway in the Cerebral Cortex cont.
•
•
Cells within a column process similar information, e.g, they
may respond best to lines of a single orientation
Are visual cortex cells in V1 and V2 feature detectors?
– yes, prolonged exposure fatigues cells
– but, cells that respond to single bar respond more to
gratings of bars or lines suggesting neurons respond to
spatial frequencies, not bars or edges
– perhaps a series of spatial frequency detectors could
represent anything we see
– still not a full explanation and object perception is still a
puzzle
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
37 of 48
Shape Analysis Beyond Area V1
•
•
•
In area V2 some cells respond to circles, lines at right angles
or other complex patterns
In V4, many cells respond to the slant of a line in threedimensional space
Shape constancy detected in inferior temporal complex
– responds selectively to complex shapes
– detects objects based on shape, not light or darkness
– responds equally strong to mirror images
• but that may interfere with reading where we need to
treat mirror image letters differently, e.g, b and d
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
38 of 48
Figure 6.27
Figure 6.27 Three transformations of an original drawing. In the inferior cortex, cells that respond
strongly to the original respond about the same to the contrast reversal and mirror image but not to the
figure-ground reversal. Note that the figure-ground reversal resembles the original very strongly in terms of
the pattern of light and darkness; however, it is not perceived as the same object. (Source: Based on Baylis
and Driver, 2002.)
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
39 of 48
Disorders of Object Recognition
•
•
Visual agnosia: inability to recognize some objects
– can describe object but doesn’t know what they are, e.g.,
key, stethoscope, smoking pipe
Prosopagnosia: inability to recognize faces
– can still read and recognize person by their voice
– inferior temporal cortex area, fusiform gyrus, especially
active in recognition of faces
• Also activated when recognizing other complex
shapes, e.g., cars and birds
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
40 of 48
Color, Depth and Motion Perception
•
•
•
Cells sensitive to color are found in parts of V1 known as
blobs, which also have cells that contribute to brightness
perception
Area V4 or nearby is important for color constancy
– monkeys with damage here can’t find yellow banana if
light is changed from white to blue
Cells of magnocellular path are specialized for stereoscopic
depth perception
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
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Color, Depth and Motion Perception cont.
•
•
Cells in area MT respond selectively to stimulus moving in a
particular direction regardless of size, shape or color
– motion blind people who cannot determine if objects are
moving may have damage here
Cells on MST respond best to expansion, contraction or
rotation of large visual scene
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
42 of 48
Figure 6.33
Figure 6.33 Stimuli that excite certain cells in the ventral part of area MST. Cells in this area respond
when an object moves relative to its background. They therefore react either when the background is
steady and the object moves or when the object and the background move.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
43 of 48
Visual Attention
•
Attention is dependent on amount and duration of activity in a
cortical area
– a brief response to stimulus produces activity in V1 area
– focused attention produces additional activity in V2 area
– similar focus on color or motion produces additional
activity in visual cortex area responsible for color and
motion perception
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
44 of 48
The Binding Problem Revisited
•
•
•
How does visual cortex bind color, shape and movement to
an object, e.g., a rabbit and bring it into consciousness?
– evidence for synchronized activity in both hemispheres
when an object is recognized
Some visual processing without consciousness
– “blindsight”: loss of visual field and person can still point
out objects or light in the blind field
• some healthy tissue may remain to provide blindsight
Dominant hypothesis is that consciousness is distributed
over several cortical areas
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
45 of 48
Infant Vision
•
•
•
Infants two days old already prefer to look at faces, circles
and stripes than patternless displays
Great difficulty in shifting attention up until about 6 months
In newborn mammals many properties will develop even if
the eyes are damaged or raised in darkness
– but if darkness continues, these properties diminish
– visual experience is required to maintain and fine tune
connections
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
46 of 48
Early Development
•
•
In newborn kitten, lack of stimulation:
– of one eye for 4-6 weeks and that eye became blind
– of both eyes up to three weeks still left cortex responsive
• but if for a longer period of time, loss of sharp
receptive fields is noted
Sensitive or critical period for normal vision
– if congenital blindness is not restored for years, newly
gained vision is almost useless
– removal of cataracts within 6 months of birth still leaves
deficits
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
47 of 48
Early Development cont.
•
•
Vision can be restored when kitten is deprived of vision in
one eye for only a few days
– but, kitten recovers better if normal eye is covered
– suggests using patch over normal eye for amblyopia
Alternating normal stimulation one eye at a time and cortex
learns to respond to one or the other, resulting in loss of
binocular vision
– accounts for strabismus, where eyes point in different
directions, in humans
James W. Kalat
Biological Psychology, 8th Edition
Chapter 6: Vision
48 of 48
Early Development cont.
•
•
•
Kitten became responsive only to horizontal lines when
wearing goggles with horizontal lines during sensitive period
– similar to development of astigmatism in humans, which
can be corrected if glasses are used early
Kitten became motion blind when raised with only strobe
lighting for 4-6 month period
Kitten receiving no visual stimuli became more responsive to
auditory and tactile stimuli than normal cats
– more true for children or infants than when blindness
occurs in adults