Goal Two Explain how the visual system enables us to see and by communicating with the brain to perceive the world The Visual Stimulus and the Eye Light is a form of electromagnetic energy Light travels through space in waves ID: 676761
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Slide1
Chapter 4 Section 2
The Visual System
Goal Two: Explain how the visual system enables us to see, and by communicating with the brain, to perceive the world.Slide2
The Visual Stimulus and the Eye
Light
is a form of electromagnetic energy. Light travels through space in waves
.
The
wavelength
of light is the distance from the peak of one wave to the peak of the next
.
Amplitude
is the height of the wave and it is associated with the brightness of a visual stimulus
.
Purity
is the mixture of wavelengths in light.Slide3Slide4
The Structure of the Eye
The eye is set up like a camera in that it gets the picture of the world
.
The
sclera
is the white outer part of the eye that gives the eye its shape and protects the eye from injury
.
The
iris
is the colored part of the eye
.
The
pupil
, which appears black, is the opening in the center of the iris. The iris contains muscles that allow the pupil to get larger or smaller depending on how much light is being let into the eye.Slide5
The Structure of the Eye
The
cornea
is the clear membrane on the outer part of the eye. The curved surface on the cornea bends light on the surface of the eye in order to focus it to the back of the eye
.
The
lens
is transparent and somewhat flexible. When a person is looking at an object far away, the lens has a relatively flat shape. However, when a person is looking at an object that is closer, more bending of the light is needed.Slide6
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Structure of the EyeSlide7
© 2011 The McGraw-Hill Companies, Inc.
Structure of the Eye: Retina
Rods
sensitive to even dim light, but not color
function well in low illumination
humans have ≈ 120 million rods
Cones
respond to color
operate best under high illumination
humans have ≈ 6 million conesSlide8Slide9
© 2011 The McGraw-Hill Companies, Inc.
Structure of the Eye: Retina
Fovea
densely populated with cones
vital to many visual tasks
Bipolar and Ganglion Cells
Optic Nerve
Blind Spot
where optic nerve leaves the eyeball
perception involves top-down processingSlide10
© 2011 The McGraw-Hill Companies, Inc.
Structure of the Eye: RetinaSlide11
© 2011 The McGraw-Hill Companies, Inc.
Visual Processing
Pathway of Visual Information
optic nerve
o
ptic chiasm
… v
isual cortex
Optic Chiasm: Optic Nerve Fibers Divide
left visual field
right hemisphere
right visual field
left hemisphere
Primary Visual Cortex
occipital lobe
initial visual processingSlide12
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Visual ProcessingSlide13
© 2011 The McGraw-Hill Companies, Inc.
Visual Processing
Feature Detectors
highly-specialized cells in the visual cortex
size, shape, color, movement, or combination
deprivation studies: brain “learns” perception
Parallel Processing
BindingSlide14
Parallel Processing
What” and “where” are two questions that need to be answered in order for people to respond appropriately to a visual stimulus
.
The “what” pathway is in the temporal lobe and processes information about what the object is. The “where” pathway is located in the parietal lobe and processes information about an object’s location
.
Parallel processing
is a simultaneous distribution of information across different neural pathways. It helps information move rapidly through the brain.Slide15
Binding
Binding
is when the different pathways and cells bring together and integrate information
.
Through binding a person can integrate information about various parts of an object. For example, if a person sees a chair, then through binding they not only see just the chair, but they also see the size, the color, the motion, etc. of the chair.Slide16
© 2011 The McGraw-Hill Companies, Inc.
Color Vision: Theories
Trichromatic Theory
Three Types of Receptors
green
,
red
,
and
blue
cones
Color Blindness
one or more cone types is inoperativeSlide17
Color Vision: Theories
The term
color blind
refers to seeing some colors but not others. Color blindness depends on which of three kinds of cones (green, red, and blue) is not working.
The
opponent-process theory
states that cells in the visual system respond to red-green and blue-yellow colors. A cell excited by red and green could be inhibited, or a cell excited by blue and the yellow could be inhibited.Slide18
© 2011 The McGraw-Hill Companies, Inc.
Color Vision: AfterimagesSlide19
Color Vision: Theories
Afterimage
sensation remains after a stimulus is removed
trichromatic theory cannot explain afterimages
Opponent Process Theory
complementary color pairs
© 2011 The McGraw-Hill Companies, Inc.Slide20
Perceiving Shape, Depth, Motion, and Constancy
To perceive a visual stimulus, the fragments of information that the eye sends to the visual cortex must be organized and interpreted
.
The
figure-ground relationship
occurs when a person organizes the perceptual field into stimuli that stand out (figure) and those that are left over (ground
).
Gestalt psychology
explains how people naturally organize their perceptions according to certain patterns. Closure is a gestalt principle; when a person sees a disconnected or complete figure, they see a whole. Proximity is a second gestalt principle; when individuals see objects as close to each other, they tend to group them as together. The third gestalt principle is similarity; when objects are similar, individuals tend to group them together.Slide21
© 2011 The McGraw-Hill Companies, Inc.
Visual Perception
organizing and interpreting visual signals
dimensions
- shape
- depth
- motion
- constancySlide22
© 2011 The McGraw-Hill Companies, Inc.
Visual Perception: Shape
Gestalt Psychology
perceptions are naturally organized according to certain patterns
whole is different from the sum of the parts
Gestalt Principles
figure-ground relationship
closure
proximity
similaritySlide23
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Figure-Ground RelationshipSlide24
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Visual Perception: ShapeSlide25
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Visual Perception: Depth
the brain constructs perception of 3D from 2D images processed by the retina
binocular cues
- disparity
- convergenceSlide26
Depth Perception
Depth perception
is the ability to see objects in three dimensions
.
Binocular cues
are depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together. For example, if a person holds their hand over one eye and focuses on an object and then switches to cover their other eye, the switching back and forth between the eyes will cause the object to jump back and forth
.
Monocular cues are depth cues that are available from the image in one eye, either the left or the right eye. Some examples of monocular cues are: familiar size, height in the field of view, linear perspective, overlap, shading, and texture gradient.Slide27
© 2011 The McGraw-Hill Companies, Inc.
Visual Perception: Depth
Monocular Cues – Pictorial Cues
familiar size
height in the field of view
linear perspective
overlap
shading
texture gradientsSlide28
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Monocular Cues:
Shading, Texture GradientSlide29
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Monocular Cues:
Linear Perspective, Height in FieldSlide30
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Visual Perception: Motion
humans have specialized motion detectors
apparent movementSlide31
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Visual Perception: MotionSlide32
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Visual Perception: Constancy
Perceptual Constancies
recognition that objects do not physically change despite changes in vantage point and viewing conditions
sensory information (retinal image) changes, but perceptual interpretation does not
Size, Shape, and Color ConstanciesSlide33
Motion Perception
Apparent motion
occurs when an object is stationary but it is perceived as moving. An example of apparent motion is watching an IMAX movie. Two forms of apparent motion are stroboscopic motion and movement aftereffects
.
Perceptual constancy
refers to the recognition of objects as remaining stationary and unchanging even though sensory input about them is changing. There are three types of perceptual constancy: size constancy, shape constancy, and brightness constancy.