viewing the world in color. color a psychological interpretation based on wavelength, amplitude, and...

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