Vision 153-158

Structure of the Eye

We only use light energy to see.

Wavelength

• The distance from the peak of one light wave to the peak of the next.

•The distance determines the hue (color) of the light we perceive.

Intensity

The amount of energy in a light wave.

Determined by the height of the wave.

The higher the wave the more intense the light is.

Vision – front of eyeball – phase 1

Pupil- adjustable opening in the center of the eye

Iris- a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

Lens- transparent structure behind pupil that changes shape to focus images on the retina

Nearsighted Vision

Farsighted Vision

Inner eye – phase 2

Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina

Retina- the light-sensitive inner surface of the eye receptor rods and cones layers of neurons that begin the processing

of visual information

The Retina

Rods and Cones – 125 million rods to 7 million cones per eye!

• Rods – sensitive to variations in light, helps us adjust to dark. Full adjustment = 30 minutes

• Cones – sensitive to color, bright light. Full adjustment = 5 minutes

Retina’s Reaction to Light

Optic nerve- nerve that carries neural impulses from the eye to the brain

Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

Fovea- central point in the retina, around which the eye’s cones cluster. Greatest visual acuity

Blind spot

Processing from retina to the brain – phase 3

• Bipolar Cells – preliminary sensory reception area. Raw data

• Ganglion cells – neurons that are photoreceptive – processes fine details from cones

• From retina cells go to optic nerve and then optic chiasm

158-163Color Processing

Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors

red green blue

Color-Deficient Vision

People who suffer red-green blindness have trouble perceiving the number within the design

Visual Information Processing

Opponent-Process Theory- opposing retinal processes enable color vision

“ON” “OFF”

red green

green red

blue yellow

yellow blue

black white

white black

Opponent Process Theory – Afterimage effect

Feature Detection

The concept that specific nerve cells in the brain respond to specific features of the stimulus, such

as shape, angle, or movement.

Parallel Processing• The processing of several aspects of a

problem simultaneously.

Color Motion Form Depth