Unit IV:Sensation & Perception

Module 18

Vision

The Eye 18-1

Visible Light

What we see as visible light is but a thin slice of the whole spectrum of electromagnetic radiation.

VisibleSpectrum

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Physical Characteristics of Light

Two physical characteristics of light help determine our sensory experience of them:

1. Wavelength (the distance from one wave peak to the next) determines hue or color

2. Intensity (the amount of energy in light waves) influences brightness

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Wavelength (hue/color)

Blue color with varying levels of intensity.As intensity increases or decreases, blue color

looks more “washed out” or “darkened.”

Violet Indigo Blue Green Yellow Orange Red

Short wavelengths

Long wavelengths

Intensity (Brightness)

18-1Wavelength & Intensity

Structure of the Eye 18-1

The Retina’s Reaction to Light 18-1

Visual Information Processing 18-2

Visual Processing 18-2

Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

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Visual Information Processing

Processing of several aspects of the stimulus simultaneously is called parallel processing.

The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

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Summary of Visual Processing 18-2

Visual Information Processing 18-3

Color Vision

Young-Helmholtz trichromatic theory: Thomas Young and Hermann von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors in the 19th century. Years later, researchers confirmed this theory.

The retina has three types of color receptors, each sensitive to one of three colors.

When we stimulate combinations of these cones, we see other colors.

For example, when both red-sensitive and green-sensitive cones are stimulated, we see yellow.

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Color Blindness

Genetic disorder in which people are blind to green or red colors.

This supports the Trichromatic theory.

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Opponent Colors

Gaze at the middle of the flag for about 30 seconds. When it disappears, stare at the dot and report

whether or not you see Britain's flag.

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