Understanding Psychology (10th Ed)

sensation p. 99
perception p. 99
stimulus p. 99
psychophysics p. 99
absolute threshold p. 100
difference threshold (just 
noticeable difference) p. 101
Weber’s law p. 102
adaptation p. 102
E VA LU AT E
1.
is the stimulation of the sense organs; 
is the sorting out, interpretation, analysis, and 
integration of stimuli by the sense organs and the brain.
2.
The term absolute threshold refers to the 
inten-
sity of a stimulus that must be present for the stimulus to 
be detected.
3.
Weber discovered that for a difference between two stim-
uli to be perceptible, the stimuli must differ by at least a 
proportion.
4.
After completing a very diffi cult rock climb in the morn-
ing, Carmella found the afternoon climb unexpectedly 
easy. This example illustrates the phenomenon of 
.
R E T H I N K
1.
Do you think it is possible to have sensation without 
perception? Is it possible to have perception without 
sensation?
2.
From the perspective of a manufacturer: How might you need 
to take psychophysics into account when developing new 
products or modifying existing ones?
Answers to Evaluate Questions
1. 
Sensation; perception; 
2.
smallest; 
3. 
constant;
4. 
adaptation
 
Module 10 
Sensing the World Around Us 
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 104
If, as poets say, the eyes provide a window to the soul, they also provide us with a 
window to the world. Our visual capabilities permit us to admire and to react to 
scenes ranging from the beauty of a sunset, to the confi guration of a lover’s face, to 
the words written on the pages of a book. 
Vision starts with light, the physical energy that stimulates the eye. Light is a 
form of electromagnetic radiation waves, which, as shown in Figure 1, are mea-
sured in wavelengths. The sizes of wavelengths correspond to different types of 
energy. The range of wavelengths that humans are sensitive to—called the visual 
spectrum —is relatively small. Many nonhuman species have different capabilities. 
For instance, some reptiles and fi sh sense energies of longer wavelengths than 
humans do, and certain insects sense energies of shorter wavelengths than humans 
do. For example, bees are attracted to fl owers that refl ect ultraviolet rays that 
humans can’t detect. 
Light waves coming from some object outside the body (such as the tree in 
Figure 2) are sensed by the only organ that is capable of responding to the visible 
spectrum: the eye. Our eyes convert light to a form that can be used by the neurons 
that serve as messengers to the brain. The neurons themselves take up a relatively 
small percentage of the total eye. Most of the eye is a mechanical device that is 
similar in many respects to a nonelectronic camera that uses fi lm, as you can see in 
Figure 2. 
Despite the similarities between the eye and a camera, vision involves processes 
that are far more complex and sophisticated than those of any camera. Furthermore, 
once an image reaches the neuronal receptors of the eye, the eye/camera analogy 
ends, for the processing of the visual image in the brain is more refl ective of a com-
puter than it is of a camera.