nanometers, (2) 500 nanometers, and (3) 400 nanometers. The first wavelength,
750 nanometers, induces the sensation we call “red.” The second, 500 nanometers,
induces the sensation we call “green.” And 400 nanometers induces the sensation
we call “violet.” The language in the preceding sentences has been carefully cho-
sen in order to make it clear that the “color” is notin the stimulus itself (i.e., a light
wave), but is produced by the firing of a certain kind of photoreceptor.
The trichromatic theory also accounts for the sensation of colors other than the
three primary ones. The sensation of orange, for example, takes place because a wave-
length of light such as 650 nanometers will cause the simulataneous firing of some
neurons that usually fire at 750 nanometers and some that fire at 500 nanometers.
White light is sensed when all of the wavelengths arrive at the retina in a ran-
dom or scrambled fashion. This causes the simultaneous firing of all three kinds of
cones. It is often pointed out that the trichromatic theory works very well. It is
the basis upon which color television sets are constructed.
(a) A leading theory of color vision is the.
(b) White light is sensed when all of the wavelengths arrive at the retina in a.
Answers: (a) trichromatic theory; (b) random or scrambled fashion.
However, there are flaws in the trichromatic theory. For example, people who
are red-green blind, lacking the two kinds of required photoreceptors, would not
be predicted to sense yellow—yet they seem to have a normal capacity to sense
yellow. As a consequence, other theories of color perception have been proposed.
They have not received the level of acceptance of the trichromatic theory; but it
is important to recognize that this major theory may explain some, but not all, of
what is involved in the physiology of color vision.
There are three basic sensations associated with vision. First, the sensation of
huesimply indicates, as already described, that we can see a range of colors. Sec-
ond, the sensation ofbrightnessindicates that we can see that objects are white
or gray or black. We can also see that they are in low or high illumination. Third,
the sensation ofsaturationindicates that we can see how richly or deeply a color
seems to soak into an object.
The three basic sensations associated with vision are.
Answer: hue, brightness, and saturation.
Hearing: The Sound of Music
If you enjoy hearing music, you appreciate the importance of the sense of hear-
ing. Also, a moment’s reflection helps us to realize that hearing is the primary way
Sensation: Studying the Gateways of Experience 49
