Vision and Visual Perception
Chapter 10
Light and the Visual Apparatus
Color Vision
Form Vision
The Perception of Objects, Color, and Movement
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Light and the Visual Apparatus
The Visible Spectrum
Figure 10.1: The Electromagnetic Spectrum
•Electromagnetic Spectrum
• Includes a variety of energy forms.
• Visible light (adequate stimulus for vision) only 1/70th of spectrum
• Light is described by its wavelength, which we associate with color
• Visible light ranges from about 300 nm to 800 nm.
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Light and the Visual Apparatus
The Eye and Its Receptors
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Light and the Visual Apparatus
Figure 10.2: The Human Eye
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Light and the Visual Apparatus
Focusing begins at the Cornea, and is completed by the Lens.
The Eye and its *Receptors. Figure 10.2: The Human Eye
Figure 10.3: The Cells of the Retina
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Light and the Visual Apparatus
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Light and the Visual Apparatus
SOURCE: (right) Adapted from “Organization of the Primate Retina,” by J. E. Dwoling and B. B. Boycott, Proceedings of the Royal
Society of London, B166, Fig. 23 on p. 104. Copyright 1966 by the Royal Society. Used with permission of the publisher and the
author.
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Light and the Visual Apparatus
Rod System
Photopigment
Function
• Rhodopsin
• Functions best in dim light,
poorly or not at all in bright
light.
• Detail vision is poor.
• Does not distinguish colors.
Cone System
• Iodopsin
• Functions best in bright light,
poorly or not at all in dim light.
• Detail vision is good.
• Can distinguish among colors
thanks to 3 different types,
each with one type of
photopigment.
Light and the Visual Apparatus
Location
Receptive Field
• Mostly in periphery of retina
• Mostly in *fovea and
surrounding area
• Large, due to convergence on
ganglion cells;
• contributes to light sensitivity.
• Small, with one or a few cones
converging on a single ganglion
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cell;
• contributes to detail vision.
The Eye and its *Receptors. Table 10.1: Summary of the
Characteristics of the Rod and Cone Systems.
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Light and the Visual Apparatus
The Eye and its Receptors
Figure 10.3: The Cells of the Retina
• Receptors:
• Normally inhibit bipolars
(glutamate) • Light turns
them off • Bipolars:
• Released from inhibition
• Stimulate ganglion cell
• Inhibition of neighbor
cells
(contrast)
Light and the Visual Apparatus
• Horizontal cells
• Amacrine cells
We have 126 million receptors, but only 1 million axons in
the optic nerve... so we need to do quite a bit of ‘data
reduction’.
The Eye and its Receptors
• The area of the retina from which a ganglion cell
(or any other cell in the visual system) receives its
input is the cell’s receptive field.
• Receptive fields of cones are small.
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Light and the Visual Apparatus
• Few cones are attached to each ganglion cell; in fovea, each
cone has its own ganglion cell.
• As a result, visual acuity—the ability to distinguish
details— is greatest in the fovea, and decrease toward the
periphery.
• Receptive fields of rods are larger.
• Many rods share each ganglion cell, enhancing sensitivity
to light but reduced visual acuity
• More numerous in the periphery, absent in the fovea.
Pathways to the Brain.
Figure 10.4: Projections From the Retinas to the Cerebral
Hemispheres.
Light and the Visual Apparatus
•Ganglion cell axons form two
optic nerves.
•Blind spot where they exit the
retina.
•Optic nerves join for a short
distance at the optic chiasm.
•Left visual field to right brain
•Right visual field to left brain
•Nerves synapse in the lateral
geniculate nuclei (LGN).
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Light and the Visual Apparatus
•LGN to Visual Cortex.
Pathways to the Brain Figure 10.5: Retinal Disparity
Light and the Visual Apparatus
• The separation
between eyes
produces retinal
disparity.
• Distant objects toward the
nasal side (B).
• Closer objects toward the
temporal retina (C).
• Provides information on
object’s distance
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Light and the Visual Apparatus
• Anterior Parietal: shape, location, and distance >
3D location of objects
Application: Restoring Lost Vision
•Blindness
Light and the Visual Apparatus
• Often due to visual receptor
deterioration, but neural
structures remain intact.
• Sight could be restored by
replacing the receptors with
an artificial retina.
• Alpha IMS (right)
SOURCE: This figure was adapted from two images at the manufacturer’s (Second Sight) website: http://2sight.eu/en/systemoverview-en
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Color Vision
Trichromatic Theory.
Figure 10.6 Independence of Wavelength and Color
•Trichromatic Theory (Young-Helmholtz)
• The primary colors in this theory are red, green, and blue.
• Observers cannot resolve these colors into separate components.
• TV and computer screens use this “RGB” processing
Color Vision
Opponent Process Theory Figure 10.7: The Color Circle
• Opponent Process Theory
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Color Vision
• R/G cone photopigment
• Broken down by red light •
Regenerates in green light.
• Y/B cone photopigment
• Broken down in yellow light
• Regenerates in blue light.
• This theory explained
• Yellow as a primary color
• Complementary colors
• Negative Color Aftereffect
• But not found in any physiological study
Color Vision
Opponent Process Theory
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Color Vision
Figure 10.8: Complementary Colors and Negative Color Aftereffect
Color Vision
Figure 10.9: Mixing Lights is Additive, Mixing Paints Is Subtractive.
Lights
Paints
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Color Vision
Figure 10.10: Hurvich & Jameson’s Proposed Interconnections of Cones
Provide Four Color Responses & Complimentary Colors
Color Vision
•
Combined trichromatic theory and opponent process
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Color Vision
•
theory:
Three receptors (Tri in Trichromatic) like pixels in TVs.
• Red
• Green
• Blue
•
Three ganglion types explains why we see yellow as a
primary.
• Yellow/Blue
• Red/Green
• Black/White (not shown)
Color Vision
A Combined Theory
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Color Vision
Color Vision
A Combined Theory. Figure 10.11: Relative Absorption of Light of
Various Wavelengths by Visual Receptors
•Support for Combined Theory
• Peak responses in cone receptors (RGB)
• Paired ganglion cells in monkey
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Color Vision
SOURCE: Adapted from “Visual Pigments of Rods and Cones in Human Retina,” by Bowmaker and Dartnall, 1980, Journal of
Physiology, 298, pp. 501–511. Copyright 1980, with permission from John Wiley & Sons, Inc.
Color Vision
A Combined Theory
Figure 10.12: Receptive Fields of Color-Opponent Cells
• Some have retinal fields made up of complementary
color circles of cones.
• Color-opponent circular fields increase color
discrimination and contrast through lateral
inhibition.
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SOURCE: Based on the findings of De Valois et al. (1966).
Color Vision
Color Blindness
Figure 10.13: A Test for Color Blindness.
•Colorblindness
•Helped
researchers
understand color vision
processes.
•People who lack one or
more cone types as a
result of a sex linked
gene.
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SOURCE: Ishihara Plate
Color Vision
Color Blindness.
•Dichromacy (missing
1 cone type)
(missing 2)
•Achromatopsia (no
cones)- very rare
• Red (Protanopia)
• Green (Deuteranopia)
• Blue (Tritanopia)
•Monochromacy
SOURCE: Wikipedia entry for “Color Blindness”
Normal vision
Protanopia perception of same
image
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Form Vision
Retinotopic Map.
Figure 10.14: Deoxyglucose Autoradiograph Showing Retinotopic
Mapping in Visual Cortex
Form Vision
Do you remember how autoradiography works? Chapter 4…
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Form Vision
SOURCE: Reprinted with permission from R. B. H. Tootell et al., “Deoxyglucose Analysis of Retinotopic Organization in Primate
Striate Cortex,” Science, 218, pp. 902–904. Copyright 1982 American Association for the Advancement of Science (AAAS).
Contrast Enhancement & Edge Detection
•Form Vision:
• Detection of an object’s boundaries and features (such as
texture).
•Retinotopic map in visual cortex
• Adjacent retinal receptors activate adjacent cells in the
visual cortex.
• But doesn’t explain form vision
Form Vision
•Contrast Enhancement & Edge Detection
• Lateral Inhibition by horizontal
• Ganglion receptive field
• Light in Center increases firing
• Light in Surround decreases firing
cells
-
+
Contrast Enhancement & Edge Detection.
Figure 10.15: Demonstration of Lateral Inhibition
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Form Vision
Form Vision
SOURCES: (a) Based on Hermann (1870). (b) From Mach Bands: Quantitative Studies on Neural Networks in the Retina (fig. 3.25. p.
107), by F. Ratcliff, 1965. San Francisco: Holden-Day. Copyright © Holden-Day Inc.
Contrast Enhancement & Edge Detection
Figure 10.16: Neural Basis of the Mach Band Illusion
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Form Vision
Contrast Enhancement & Edge Detection
Form Vision
Figure 10.17: Effect of Light on Center and Surround of Receptive Field
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Form Vision
•On-center cells
Form Vision
• Light in center increases firing
• Light in surround reduces firing below spontaneous rate
•Off-center cells
• Light in surround increases firing or excitation.
• On surrounds
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Form Vision
Contrast Enhancement & Edge Detection. Figure 10.18: Effects of a Border
on an On-Center and an Off-Center Ganglion Cell
•On-center ganglion
•A–C
•Off-center ganglion
•D
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Form Vision
FIGURE 10.19 Responses to Lines at Different Orientations in a
*Simple Cell Specialized for Vertical Lines.
•Response greatest when
line closest to preferred
vertical orientation
(middle and bottom)
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SOURCE: From “Receptive Fields of Single Neurons in the Cat’s Striate Cortex,” by D. H. Hubel and T. N. Wiesel, 1959, Journal of
Physiology, 148, pp. 574–591, Fig 3. © 1959 by The Physiology Society. Reprinted by permission.
Form Vision
Hubel and Wiesel’s Theory
Figure 10.20: Hubel and Wiesel’s Explanation for Responses of Simple
Cells
•Simple cells of Visual
Cortex
• Input: ganglion cells with
linear overlap of
receptive fields
• Respond to line or edge
at a specific
• Orientation
• Place on the retina.
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Hubel & Wiesel’s Complex Cells
Figure 10.21
• Complex cells of visual cortex
• Input from simple cells with
same field orientations near
each other
• Position changes, but not
orientation changes
• Accounts for boundary
detection
• Questionable whether
these process surface
details.
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Form Vision
See Figure 10.22: Illustration of High and Low Frequencies in a
Visual Scene
•Spatial Frequency Theory
•Cortical cells perform Fourier analysis on
luminosity
•Different cells have a variety of sensitivities
•Can detect edges AND gradations of change.
SOURCES: (a and b) Reprinted with permission from L. D. Harmon and B. Julesz, “Masking in Visual Recognition: Effects of Two-Dimensional Filtered Noise,”
Science, 180, pp. 1194–1197. Copyright 1973 American Association for the Advancement of Science (AAAS). (c) Gala Contemplating the Mediterranean Sea
Which at Twenty Meters Becomes the Portrait of Abraham Lincoln-Homage to Rothko (Second version). 1976. Oil on canvas. 75.5 x 99.25 inches. © 2010
Salvador Dalí, Gala-Salvador Dalí Foundation/Artists Rights Society (ARS), New York.
Form Vision
Figure 10.23: The Role of High and Low Frequencies in Vision
• High frequency transitions are not very meaningful.
• Gradual transitions (low frequencies) are more
recognizable.
• Researchers have found cortical cells that respond to light-dark “gratings”
containing a specific combination of frequencies.
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Original
Picture
Low Frequencies
Removed
High Frequencies
Removed
Perception of Objects, Color, &
Movement
•Modular processing
• segregation of the brain functions into separate
locations (area specific specialization)
•Hierarchical processing
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Perception of Objects, Color, &
• information is processed by ascending through
increasingly complex levels of the nervous system
•Distributed processing
• Processing occurs across a wide area of the brain.
•Another view is that, like language, vision is a mix of
modular and distributed processing.
Movement
Two Pathways of Visual Analysis
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Perception of Objects, Color, &
•Parvocellular system
• Parvocellular ganglion cells located in the fovea.
• Small, color-opponent circular receptive fields
• Discrimination of fine detail and color (Visual Acuity)
•Magnocellular system
• Ganglion cells in the periphery
• Large, brightness-opponent receptive fields
• Fast on, fast off
• Brightness contrast and movement
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Perception of Objects, Color, &
Movement
Figure 10.25: The Ventral “What” Stream of Visual Processing
• Ventral Stream (“What”)
• Parvocellular system to V1
• V1 through V2 to V4, then to inferior temporal and prefrontal cortices
• Color perception, object recognition
• Damage:
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Perception of Objects, Color, &
See,
reach for,
and walk
around
objects, but
they can’t
identify
•
them.
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Perception of Objects, Color, &
Movement
Figure 10.25: The Dorsal “Where” Stream of Visual Processing
• Dorsal stream (“Where”)
• Magnocellular system to V1
• V1 to V5/MT and MST, then to posterior parietal and prefrontal
cortices
• Movement and location of objects in space
• Damage
• Identify, but trouble looking at, reaching for, grasping objects using
vision
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Perception of Objects, Color, &
Movement
•Both systems then meet in the prefrontal cortex.
• Manages information in memory while it is being used.
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Perception of Objects, Color, &
• For example, it integrates information about the body and
about objects while planning movements.
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Disorders of Visual Perception
Figure 10.25: The Ventral “What” and Dorsal “Where” Streams of Visual
Processing
•Inferior Temporal Area
• Cells specific for geometric figures, houses, faces, hands,
words…
• Likely receives input from cells with narrower sensitivities.
• Capabilities may be “hardwired,” but learning is required
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Disorders of Visual Perception
Figure 10.26: Stimuli Used to Produce Responses in “Hand-” and “Face-”
Sensitive Cells in Monkeys.
•Cells in IT cortex of macaque
Disorders of Visual Perception
• Hand-like shapes better than other shapes (top)
• Also have face-sensitive cells (bottom)
SOURCES: (a) From “Visual Properties of Neurons in Inferotemporal Cortex of the Macaque,” by C. G. Gross et al., 1972, Journal of
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Disorders of Visual Perception
Neurophysiology, 35. Reprinted with permission. (b) From “Stimulus-Selective Properties of Inferior Temporal Neurons in the Macaque,” by R.
Desimone et al., Journal of Neuroscience, 4, pp. 2057 Copyright © 1984 Society for Neuroscience. Reprinted with permission.
Figure 10.26b: Stimuli Used to Produce Responses in “Hand-” and “Face” Sensitive Cells in Monkeys.
•Object Agnosia
• IT Cortex damage
• Cannot identify objects
Disorders of Visual Perception
SOURCE: (b) From “Stimulus-Selective Properties of Inferior Temporal Neurons in the Macaque,” by R. Desimone et al., Journal of
Neuroscience, 4, pp. 2057 Copyright © 1984 Society for Neuroscience. Reprinted with permission.
Figure 10.27: Location of Brain Damage in Patients With Prosopagnosia
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Disorders of Visual Perception
•Prosopagnosia- inability
to recognize familiar
faces.
• Fusiform Face Area (FFA, of
IT cortex), R side
• Genetic link to deficits in
frontal & temporal lobes in
small number of cases
• Greeble Study
• FFA responsible for
nonhuman face recognition
Disorders of Visual Perception
SOURCE: From “Behavioral Deficits and Cortical Damage Loci in Cerebral Achromatopsia,” by S. E. Bouvier and S. A. Engel, 2006,
Cerebral Cortex, 16, pp. 183–191.
Figure 10.28: Activity in Fusiform Face Area while Viewing Faces &
Greebles
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Disorders of Visual Perception
•Prosopagnosia
• Fusiform Face Area
(FFA, of IT cortex), R side
• Genetic link to deficits in
frontal & temporal lobes
in small number of cases
• Greeble Study
• FFA responsible for nonhuman face recognition
Disorders of Visual Perception
SOURCE: From “Activation of the Middle Fusiform ‘Face Area’ Increases With Expertise in Recognizing Novel Objects,” I. Gauthier et
al., Nature Neuroscience, 2, 568–573. Copyright © 1999 Macmillan Publishers. Used with permission.
Face Blindness and Blindsight
•Blindsight
• Damage to V1 causes cortical blindness, BUT
• Superior colliculus also connects to striate cortex
independently
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Disorders of Visual Perception
• Therefore, individuals can react unconsciously to stimuli
without “seeing” them
•Visual word form area (VWFA)
• Responds to written words
Color and Movement Agnosias
•Color agnosia is the loss of the ability to perceive
colors
• V1 is wavelength coded
Disorders of Visual Perception
• V4 is color coded and provides color constancy
SOURCE: http://blogs.scientificamerican.com/streams-of-consciousness/2011/12/13/an-artist-reveals-how-he-trickstheeyesSOURCE: http://blogs.scientificamerican.com/streams-of-consciousness/2011/12/13/an-artist-reveals-how-he-tricks-theeyes/
Image© James Curney
Color and Movement Agnosias
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Disorders of Visual Perception
•Movement agnosia is the inability to perceive
movement.
•Information about movement is integrated in area
MT.
•Patient LM had difficulty:
• Guiding eye and finger movements
• Telling if something (or someone) was moving
• Objects moving toward or away from him
Neglect and the Role of Attention
Figure 10.29: Drawings Copied by a Left-Field Neglect Patient
Disorders of Visual Perception
• Neglect
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Disorders of Visual Perception
• Posterior Parietal Cortex damage (R side)
• Input from the visual, auditory, and somatosensory areas
• Locate and ATTEND to objects in space
• Orient the body in the environment.
• Ignores the contralateral world completely (but reports
normal vision)
SOURCE: From Brain, Mind, and Behavior (2nd ed.; p. 300), by F. E. Bloom and A. Lazerson. © 1988 W. H. Freeman & Co.
The Problem of Final Integration
The Binding Problem
•Binding:
• How the brain combines information from different
areas into an integrated experience
•Areas it might occur:
• Superior Temporal Gyrus
• receives input from both dorsal and ventral streams.
• Parietal cortex
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• damage causes neglect.
• Prefrontal areas
• Where both streams finally merge and decisions are
made
The Problem of Final Integration
The Binding Problem
APPLICATION: When Binding Goes Too Far
•Overbinding:
• Synesthesia
• Stimulation in one sense triggers an experience in another
• Activity increases in V4 during color synesthesia.
• Grapheme/color- more connections in visual integration areas.
SOURCE: From J. A. Nunn et al., “Functional Magnetic Resonance Imaging of Synesthesia: Activation of V4/V8 by Spoken Words,”
Nature Neuroscience, 5, 371–375. Copyright © 2002 Macmillan Publishers. Used with permission.
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