VIEWING THE
WORLD IN COLOR
COLOR
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A psychological interpretation
Based on wavelength, amplitude, and purity
Humans can discriminate among c. 10 million colors
Variations are a result of mixing…
COLOR
• Subtractive mixing: removing some wavelengths of light,
leaving less light than was originally there
• Additive color: superimposing lights, putting more light in the
mixture than exists in any one light itself
TRICHROMATIC THEORY OF
COLOR VISION
• Holds that the human eye has 3 types of receptors with
differing sensitivities to different light wavelengths
• Helmholtz: red, green, and blue---the primary colors
COLOR BLINDNESS
• Encompasses a variety of deficiencies in the ability to
distinguish among colors
• More frequent in males
• Most are dichromats
OPPONENT PROCESS THEORY
OF COLOR VISION
• Holds that color perception depends on receptors that make
antagonistic responses to 3 pairs of colors
• Complementary colors: colors that produce gray tones when
mixed together
• Afterimage: a visual image that persists after a stimulus is
removed
RECONCILING THEORIES OF
COLOR VISION
• It takes both theories to explain color vision
• George Wald: eye has 3 types of cones---trichromatic theory
• DeValois: cells throughout the eye respond in opposite ways
to red vs. green and blue vs. yellow---opponent process
PERCEIVING FORMS,
PATTERNS, AND OBJECTS
• Reversible figure: a drawing that is compatible w/2
interpretations that can shift back and forth
• Demonstrates same visual input can result in radically
different perceptions
• Perceptual set: a readiness to perceive a stimulus in a
particular way
FEATURE ANALYSIS
• The process of detecting specific elements in visual input and
assembling them into a more complex form
BOTTOM-UP/TOP-DOWN
• Bottom-up processing: a progression from individual elements
to the whole
• Top-down processing: a progression from the whole to the
elements
LOOKING AT THE WHOLE:
GESTALT PRINCIPLES
• The whole can be more than the sum of its parts
• Phi phenomenon: the illusion of movement created by
presenting visual stimuli in rapid succession
GESTALT PRINCIPLES
• Figure and ground: figure is thing being looked at and ground
is the background
• Figures have more substance and shape, and appear closer
GESTALT PRINCIPLES
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Proximity: things near one another seem to belong together
Similarity: we group things that are similar
Continuity: tendency to follow the direction you are led
Simplicity: organize in simplest way possible
Closure: group in order to create completeness
FORMULATING PERCEPTUAL
HYPOTHESES
• Distal stimuli: stimuli that lie in the distance (outside the body)
• Proximal stimuli: the stimulus energies that impinge directly
on sensory receptors
• Perceptual hypothesis: an inference about which distal stimuli
could be responsible for the proximal stimuli sensed
PERCEIVING DEPTH AND
DISTANCE
• Depth perception: interpretation of visual cues that indicate
how near or far away objects are
• We rely on different clues classified in 2 types…
BINOCULAR CUES
• Def: clues about distance based on the differing views of the 2
eyes
• Principle depth cue is retinal disparity: the fact that objects
within 25 ft project images to slightly different locations on
the right and left retinas, so the right and left eyes see slightly
different views of the object
• Another cue is convergence: sensing the eyes converging
toward each other as they focus on closer objects
MONOCULAR CUES
• Def: clues about distance based on the image in either eye
alone
• Motion parallax: images of objects at different distances
moving across the retina at different rates
MONOCULAR CUES
• Pictorial depth cues: clues about distance that can be given in
a flat picture
• Includes linear perspective, texture gradients, interposition,
relative size, height in plane, and light and shadow
PERCEPTUAL CONSTANCIES
IN VISION
• Perceptual constancy: a tendency to experience a stable
perception in the face of continually changing sensory input
OPTICAL ILLUSIONS
• Def: an apparently inexplicable discrepancy btwn the
appearance of a visual stimulus and its physical reality
• Müller-Lyer Illusion
• Ponzo Illusion
• Shepard Illusion
• Ames Room
IMPOSSIBLE FIGURES
• Def: objects that can be represented in 2 dimensional pictures
but cannot exist in 3 dimensional space