Invitation to Psychology

194 Chapter 6 Sensation and Perception

3

Saturation (colorfulness) is the dimension of

visual experience related to the complexity of

light—that is, to how wide or narrow the range

of  wavelengths is. When light contains only a

single wavelength, it is said to be pure, and the re-

sulting color is completely saturated. At the other

extreme, white light contains all the wavelengths

of visible light (corresponding to all the colors in

the visible spectrum) and has zero saturation. Black

is a lack of any light at all (it has no color) and so

it is also completely unsaturated. In nature, pure

light is extremely rare. We usually sense a mixture

of wavelengths, and as a result see colors that are

duller and paler than completely saturated ones.

Variations in brightness

Variations in saturation

Variations in hue

an eye on the World Lo 6.7, Lo 6.8,

Lo 6.9

Light enters the visual system through the eye,

a wonderfully complex and delicate structure. As

you read this section, examine Figure 6.2. Notice

that the front part of the eye is covered by the

transparent cornea. The cornea protects the eye

and bends incoming light rays toward a lens lo-

cated behind it. A camera lens focuses incoming

light by moving closer to or farther from the shut-

ter opening. However, the lens of the eye works by

subtly changing its shape, becoming more or less

curved to focus light from objects that are close

by or far away. The amount of light that gets into

the eye is controlled by muscles in the iris, the part

of the eye that gives it color. The iris surrounds

the round opening, or pupil, of the eye. When you

enter a dim room, the pupil widens, or dilates, to

let more light in. When you emerge into bright

sunlight, the pupil gets smaller, contracting to al-

low in less light.

The visual receptors are located in the back of

the eye, or retina. (The retina also contains special

cells that communicate information about light

saturation Vividness
or purity of color; the
dimension of visual expe-
rience related to the com-
plexity of light waves.

retina Neural tissue
lining the back of the
eyeball’s interior, which
contains the receptors for
vision.

You are about to learn...

•    how the physical characteristics of light waves

correspond to the psychological dimensions of

vision.

•    the basics of how the eye works, and why the

eye is not a camera.

•    how we see colors, and why we can describe a

color as bluish green but not as reddish green.

•    how we know how far away things are.

•    why we see objects as stable even though

sensory stimulation from the object is constantly

changing.

•    why studying illusions is not only fun but also

valuable.

Vision

More information about the external world

comes to us through our eyes than through any

other sense organ. Because we evolved to be most

active in the daytime, we are equipped to take

advantage of the sun’s illumination. Animals that

are active at night tend to rely more heavily on

hearing.

What We See Lo 6.6

The stimulus for vision is light; even cats, rac-

coons, and other creatures famous for their ability

to get around in the dark need some light to see.

Visible light comes from the sun and other stars

and from lightbulbs, and it is also reflected off

objects. The physical characteristics of light affect

three psychological dimensions of our visual world:

hue, brightness, and saturation.

1

Hue, the dimension of visual experience speci-

fied by color names, is related to the wavelength

of light—that is, to the distance between the crests

of a light wave. Shorter waves tend to be seen as

violet and blue, longer ones as orange and red.

The sun produces white light, which is a mixture

of all the visible wavelengths. Sometimes, drops of

moisture in the air act like a prism: They separate

the sun’s white light into the colors of the visible

spectrum, and we are treated to a rainbow.

2

Brightness is the dimension of visual experi-

ence related to the amount, or intensity, of

the light an object emits or reflects. Intensity cor-

responds to the amplitude (maximum height) of

the wave. Generally speaking, the more light an

object reflects, the brighter it appears. However,

brightness is also affected by wavelength: Yellows

appear brighter than reds and blues even when

their physical intensities are equal.

hue The dimension of
visual experience speci-
fied by color names and
related to the wavelength
of light.

brightness Lightness or
luminance; the dimen-
sion of visual experience
related to the amount
(intensity) of light emit-
ted from or reflected by
an object.