Lesson 6: Vision

hue

dimension of color as determined by the wavelength of light

rods

retinal photoreceptors that detect black, white, and gray, and are sensitive to peripheral vision and movement

fovea

central focal point in the retina, around which the eye’s cones cluster

lens

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

opponent-process theory

theory that opposing retinal processes (red-green, blue-yellow, white-black) enable color vision

wavelength

distance between peaks of waves, for sound or light

cornea

protective, clear outer layer that covers the pupil and iris

accomodation

process by which the eye’s lens changes shape to focus images of near or far objects on the retina

retina

light-sensitive back inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

iris

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

optic nerve

nerve that carries neural impulses from the eye to the brain; made up of ganglion cells

intensity

amount of energy in a light wave as determined by the wave’s amplitude

intensity influences what one perceives as…

brightness

blind spot

point at which the optic nerve leaves the eye; no receptor cells are located there

cones

retinal photoreceptors that detect detail and color, and function in bright light, including daylight

pupil

adjustable opening in the center of the eye through which light enters

Young-Helmholtz trichromatic theory

theory that the retina contains sensitivity to three color receptors (red, green, and blue) and, when stimulated in combination, the perception of any color is created

how does light enter the eye?

light enters the eye through the cornea, which bends light to help provide focus; the light then passes through the pupil and hits the transparent lens; the lens changes its shape and thickness to focus in accomodation; the lens then focuses the light rays into an upside-down image on the retina

what happens to a light-energy particle after it reaches the retina?

the particle threads its way through the retina’s sparse outer layer of cells to reach the back of the eye; it then encounters the rods and cones, where the light energy triggers chemical changes; the chemical reaction sparks neural signals in nearby bipolar cells, which then activate the ganglion cells that make up the optic nerve; after briefly stopping at the thalamus, the information reaches the visual cortex

cones (number, location in retina, sensitivity in dim light, color sensitivity, detail sensitivity)

6 million, center, low, high, high

rods (number, location in retina, sensitivity in dim light, color sensitivity, detail sensitivity)

120 million, periphery, high, low, low

feature detectors

nerve cells in the brain’s visual cortex that respond to specific features of stimuli, such as shape, angle, or movement

parallel processing

processing multiple aspects of a stimulus or problem simultaneously

1

optic nerve

3

fovea

4

retina

8

lens

9

cornea

10

pupil

12

iris