Using Knowledge: Top-Down Processing • 63accurate perception, it is potentially slow and therefore risky (what if the object actu-
ally is a dangerous animal?).
The idea of describing the operation of Gestalt principles as heuristics surprises
some people, because heuristics are most often associated with reasoning, solving prob-
lems, and making decisions. In fact, many books don’t discuss heuristics until the chap-
ter on problem solving. But doing that would miss a chance to introduce one of the
main messages of this book, which is that different types of cognition, such as percep-
tion, attention, memory, language, reasoning, problem solving, and decision making,
involve similar mechanisms.
Because all of these cognitions share the same nervous system and are outcomes of
the operation of the same mind, it shouldn’t be surprising that they have some operat-
ing principles in common. We will see, for example, when we discuss long-term mem-
ory in Chapter 8, that knowledge gained from past experiences can infl uence memory.
Thus, when a person is asked to remember a written passage describing a familiar situ-
ation, such as visiting a dentist’s offi ce, the memory report is often infl uenced by earlier
experiences the person has had in visiting the dentist. Sometimes these experiences
aid memory, and sometimes they result in errors, just as occurred in our perceptual
example when the forms in Figure 3.24 were mistaken for a creature.
In Chapters 7 and 8 we will have more to say about how our prior knowledge
affects memory. To continue our discussion of the role of knowledge in perception, we
now consider the idea that perception is infl uenced by regularities in the environment.TAKING REGULARITIES IN THE ENVIRONMENT INTO ACCOUNT
Modern perceptual psychologists have introduced the idea that perception is infl uenced
by our knowledge of regularities in the environment—characteristics of the environ-
ment that occur frequently. For example, blue is associated with open sky, landscapes
are often green and smooth, and verticals and horizontals are often associated with
buildings. We can distinguish two types of regularities, physical regularities and seman-
tic regularities.Physical Regularities Physical regularities are regularly occurring physical properties
of the environment. For example, there are more vertical and horizontal orientations
in the environment than oblique (angled) orientations. This occurs in human-made
environments (for example, buildings contain lots of horizontals and verticals) and also
in natural environments (trees and plants are more likely to be vertical or horizontal
than slanted) (Coppola et al., 1998). It is therefore no coincidence that people can
perceive horizontals and verticals more easily than other orientations, an effect called
the oblique effect (Appelle, 1972; Campbell et al., 1966; Orban et al., 1984). Another
example of a physical regularity is that when one object partially covers another one,
the contour of the partially covered object “comes out the other side,” as occurs for the
rope in Figure 3.16 and the Celtic knot in Figure 3.17.
Another physical regularity is illustrated by the following demonstration.DEMONSTRATION Shape From Shading
What do you perceive in ● Figure 3.25a? Do some of the discs look as though they are stick-
ing out, like parts of three-dimensional spheres, and others appear to be indentations? If you
do see the discs in this way, notice that the ones that appear to be sticking out are arranged
in a square. After observing this, rotate the page so the small dot is below the discs. Does this
change your perception?Figures 3.25b and c show that if we assume that light is coming from above (which
is usually the case in the environment), then patterns like the circles that are light-colored
on the top would be created by an object that bulges out, as illustrated in Figure 3.25b,Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.