world with a relatively blank slate, ready to learn what there is to learn about
the perceptual world? Most modern theorists agree that your experience of
the world consists of a combination of nature and nurture. We will see, how-
ever, that these theorists disagree on the size of the portions that make up this
combination.
Helmholtz’s Classical Theory In 1866,Hermann von Helmholtzargued for the
importance ofexperience—or nurture—in perception. His theory emphasized
the role of mental processes in interpreting the often ambiguous stimulus
arrays that excite the nervous system. By using prior knowledge of the envi-
ronment, an observer makes hypotheses, or inferences, about the way things
really are. For instance, you would be likely to interpret your brief view of
a four-legged creature moving through the woods as a dog rather than as a
wolf. Perception is thus aninductiveprocess, moving from specific images to
Figure 7.7 (continued)
Perception 145