The Visual SystemThe Visual System

A.P. PsychologyMs. Sullivan

A.P. PsychologyMs. Sullivan

LightLight

For People to see there must be light

Light - a form of electromagnetic radiation that travels as a wave

Varies in amplitude, wavelength, and purity

For People to see there must be light

Light - a form of electromagnetic radiation that travels as a wave

Varies in amplitude, wavelength, and purity

LightLight

Amplitude: height; affects perception of brightness

Wavelength: (distance between peaks) affects perception of color

Purity: (how varied the mix is) affects perception of saturation, or richness of colors

Amplitude: height; affects perception of brightness

Wavelength: (distance between peaks) affects perception of color

Purity: (how varied the mix is) affects perception of saturation, or richness of colors

The EyeThe Eye

Eye serves 2 main purposes1. Channel light to the

neural tissue that receives it

2. House the neural tissue

Eye serves 2 main purposes1. Channel light to the

neural tissue that receives it

2. House the neural tissue

The EyeThe Eye

The EyeThe Eye

Cornea: Light enters here; like a transparent window

Lens: the transparent eye structure that focuses the light rays falling on the retina

Cornea: Light enters here; like a transparent window

Lens: the transparent eye structure that focuses the light rays falling on the retina

The EyeThe Eye

Nearsightedness: close objects cannot be seen clearly but distant objects appear blurryBecause the focus of light

from distant objects falls short of the retina

Eyeball is too long

Nearsightedness: close objects cannot be seen clearly but distant objects appear blurryBecause the focus of light

from distant objects falls short of the retina

Eyeball is too long

The EyeThe Eye

Farsightedness: distant objects are seen clearly but close objects appear blurryFocus of light from close

objects fall behind the retinaEyeball is too short

Farsightedness: distant objects are seen clearly but close objects appear blurryFocus of light from close

objects fall behind the retinaEyeball is too short

The EyeThe Eye

Pupil: the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye

Retina:is the neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain

Pupil: the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye

Retina: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 EyeThe Eye

Rods: specialized visual receptors that play a key role in night vision and peripheral vision

Cones: specialized visual receptors that play a key role in daylight vision and color vision

Rods: specialized visual receptors that play a key role in night vision and peripheral vision

Cones: specialized visual receptors that play a key role in daylight vision and color vision

Pathways to BrainPathways to Brain

Optic 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

Optic 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

ColorColor

Lights people see are mixtures of various wavelengths

Perceived Color is primarily a function of the dominant wavelength in these mixtures

Lights people see are mixtures of various wavelengths

Perceived Color is primarily a function of the dominant wavelength in these mixtures

ColorColor

Long wavelengths = Red

Short wavelengths= Violet

Color is a psychological interpretation, it is not a physical property of light

Long wavelengths = Red

Short wavelengths= Violet

Color is a psychological interpretation, it is not a physical property of light

Color MixingColor Mixing

Humans can perceive about a million different colors

Most of the diverse colors are the result of mixing a few basic colors

There are two kinds of color mixing

Humans can perceive about a million different colors

Most of the diverse colors are the result of mixing a few basic colors

There are two kinds of color mixing

Color MixingColor Mixing

Subtractive Color Mixing - works by removing some wavelengths of light, leaving less light than was originally there

Subtractive Color Mixing - works by removing some wavelengths of light, leaving less light than was originally there

Additive Color Mixing - works by superimposing lights, putting more light in the mixture than exists in any one light by itself

Additive Color Mixing - works by superimposing lights, putting more light in the mixture than exists in any one light by itself

Theories of Color VisionTheories of Color Vision

1. Trichromatic Theory - the human eye has three types of receptors with differing sensitivities to different light wavelengthsRed, green, blueEye does its own color mixing

of these 3 colorsAdditive mixture of red, green

and blue fool you into seeing all the colors of a natural scene

1. Trichromatic Theory - the human eye has three types of receptors with differing sensitivities to different light wavelengthsRed, green, blueEye does its own color mixing

of these 3 colorsAdditive mixture of red, green

and blue fool you into seeing all the colors of a natural scene

Theories of Color VisionTheories of Color Vision

Color Blindness - tied to Trichromatic Theory - variety of deficiencies in distinguishing between colorsOccurs more frequently in menBlindness does not mean all colors,

most deal with only two color channels (dichromats)

Color Blindness - tied to Trichromatic Theory - variety of deficiencies in distinguishing between colorsOccurs more frequently in menBlindness does not mean all colors,

most deal with only two color channels (dichromats)

Theories of Color VisionTheories of Color Vision

Opponent Process Theory - color perception depends on receptors that make antagonistic responses to three pairs of colorsComplementary Colors - pairs

of colors that produce gray tones when mixed together

Afterimage - 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

Opponent Process Theory - color perception depends on receptors that make antagonistic responses to three pairs of colorsComplementary Colors - pairs

of colors that produce gray tones when mixed together

Afterimage - 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.

YellowYellow

If you ask people to describe colors but restrict them to using three names, they run into difficultyWould you describe “Yellow” as

“reddish green”?

Add Yellow to the 3 basic colors and people are more comfortable

If you ask people to describe colors but restrict them to using three names, they run into difficultyWould you describe “Yellow” as

“reddish green”?

Add Yellow to the 3 basic colors and people are more comfortable