Let’s Get Visual!

What We See p. 125

Hue Visual experience

specified by color names and related to the wavelength of light.

Intensity Influences

brightness and related to the amplitude of the light wave

An Eye on the World Cornea

Protects eye and bends light toward lens.

Lens Focuses on objects by

changing shape. Iris

Controls amount of light that gets into eye.

Pupil Widens or dilates to let

in more light.

The Structures of the Retina

Cones (Fewer) Rods (More)

Near fovea Located in peripheral of the retina

Responds to color

Dark-adapted vision, scotopic

More detail, higher resolution

More sensitive to light, motion

Hubel & Wiesel’s Experiment Much visual processing is done in the brain. Feature Detectors

Some cortical cells respond to lines in specific orientations

Other cells in the cortex respond to other shapes

How We See Colors Young Helmholtz Trichromatic theory Opponent process theory

Trichromatic Theory Young (1802) & von

Helmholtz (1852) both proposed that the eye detects 3 primary colors: red, blue, & green

All other colors can be derived by combining these three.

Opponent-Process Theory A competing theory of

color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic.

Opponent-Process cells are inhibited by a color, and have a burst of activity when it is removed.

What’s Happening?

In the retina of your eyes, there are 3 types of color receptors (cones) that are most sensitive to either red, blue or green.

When you stare at a particular color for too long, these receptors get "tired" or "fatigued."

When you then look at the white background, the receptors that are tired do not work as well.

Therefore, the information from all of the different color receptors is not in balance and you see the color "afterimages."

You can see that you vision quickly returns to normal.

Test of Color Deficiency