The Visual System A.P. Psychology Ms. Sullivan A.P. Psychology Ms. Sullivan

Light FFor People to see there must be light FLight - a form of electromagnetic radiation that travels as a wave FVaries in amplitude, wavelength, and purity FFor People to see there must be light FLight - a form of electromagnetic radiation that travels as a wave FVaries in amplitude, wavelength, and purity

Light FAmplitude: height; affects perception of brightness FWavelength: (distance between peaks) affects perception of color FPurity: (how varied the mix is) affects perception of saturation, or richness of colors FAmplitude: height; affects perception of brightness FWavelength: (distance between peaks) affects perception of color FPurity: (how varied the mix is) affects perception of saturation, or richness of colors

The Eye FEye serves 2 main purposes F1. Channel light to the neural tissue that receives it F2. House the neural tissue FEye serves 2 main purposes F1. Channel light to the neural tissue that receives it F2. House the neural tissue

The Eye

FCornea: Light enters here; like a transparent window FLens: the transparent eye structure that focuses the light rays falling on the retina FCornea: Light enters here; like a transparent window FLens: the transparent eye structure that focuses the light rays falling on the retina

The Eye FNearsightedness: close objects cannot be seen clearly but distant objects appear blurry FBecause the focus of light from distant objects falls short of the retina FEyeball is too long FNearsightedness: close objects cannot be seen clearly but distant objects appear blurry FBecause the focus of light from distant objects falls short of the retina FEyeball is too long

The Eye FFarsightedness: distant objects are seen clearly but close objects appear blurry FFocus of light from close objects fall behind the retina FEyeball is too short FFarsightedness: distant objects are seen clearly but close objects appear blurry FFocus of light from close objects fall behind the retina FEyeball is too short

The Eye FPupil: the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye FRetina:is the neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain FPupil: the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye FRetina:is the neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain

The Eye FRods: specialized visual receptors that play a key role in night vision and peripheral vision FCones: specialized visual receptors that play a key role in daylight vision and color vision FRods: specialized visual receptors that play a key role in night vision and peripheral vision FCones: specialized visual receptors that play a key role in daylight vision and color vision

Pathways to Brain FOptic Chiasm: the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain

Color FLights people see are mixtures of various wavelengths FPerceived Color is primarily a function of the dominant wavelength in these mixtures FLights people see are mixtures of various wavelengths FPerceived Color is primarily a function of the dominant wavelength in these mixtures

Color FLong wavelengths = Red FShort wavelengths= Violet FColor is a psychological interpretation, it is not a physical property of light FLong wavelengths = Red FShort wavelengths= Violet FColor is a psychological interpretation, it is not a physical property of light

Color Mixing FHumans can perceive about a million different colors FMost of the diverse colors are the result of mixing a few basic colors FThere are two kinds of color mixing FHumans can perceive about a million different colors FMost of the diverse colors are the result of mixing a few basic colors FThere are two kinds of color mixing

Color Mixing FSubtractive Color Mixing - works by removing some wavelengths of light, leaving less light than was originally there FAdditive Color Mixing - works by superimposing lights, putting more light in the mixture than exists in any one light by itself

Theories of Color Vision F1. Trichromatic Theory - the human eye has three types of receptors with differing sensitivities to different light wavelengths FRed, green, blue FEye does its own color mixing of these 3 colors FAdditive mixture of red, green and blue fool you into seeing all the colors of a natural scene F1. Trichromatic Theory - the human eye has three types of receptors with differing sensitivities to different light wavelengths FRed, green, blue FEye does its own color mixing of these 3 colors FAdditive mixture of red, green and blue fool you into seeing all the colors of a natural scene

Theories of Color Vision FColor Blindness - tied to Trichromatic Theory - variety of deficiencies in distinguishing between colors FOccurs more frequently in men FBlindness does not mean all colors, most deal with only two color channels (dichromats) FColor Blindness - tied to Trichromatic Theory - variety of deficiencies in distinguishing between colors FOccurs more frequently in men FBlindness does not mean all colors, most deal with only two color channels (dichromats)

Theories of Color Vision FOpponent Process Theory - color perception depends on receptors that make antagonistic responses to three pairs of colors FComplementary Colors - pairs of colors that produce gray tones when mixed together FAfterimage - a visual image that persists after a stimulus is removed; the color of the afterimage will be the compliment of the color you originally stared at FOpponent Process Theory - color perception depends on receptors that make antagonistic responses to three pairs of colors FComplementary Colors - pairs of colors that produce gray tones when mixed together FAfterimage - a visual image that persists after a stimulus is removed; the color of the afterimage will be the compliment of the color you originally stared at

The basic assumption of Opponent-Process Theory is that colors come in pairs. The "achromatic system" of black-white (brightness) and the "chromatic system" of red-green and blue-yellow. The achromatic system sees brightness contrast while the chromatic system sees color contrast. The picture above shows how the three classes of photoreceptor map on to the opponent process pairs.

Yellow FIf you ask people to describe colors but restrict them to using three names, they run into difficulty FWould you describe “Yellow” as “reddish green”? FAdd Yellow to the 3 basic colors and people are more comfortable FIf you ask people to describe colors but restrict them to using three names, they run into difficulty FWould you describe “Yellow” as “reddish green”? FAdd Yellow to the 3 basic colors and people are more comfortable