VIEWING THE WORLD IN COLOR

VIEWING THE WORLD IN COLOR

COLOR• 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• 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