in its center. Illusions at this level generally occur because the arrangement of a
stimulus array sets off receptor processes in an unusual way that generates a
distorted image.
Illusions in Reality Are illusions just peculiar arrangements of lines, colors, and
shapes used by artists and psychologists to plague unsuspecting people?
Hardly. Illusions are a basic part of your everyday life. They are an inescapable
aspect of the subjective reality you construct. And even though you may rec-
ognize an illusion, it can continue to occur and fool you again and again.
Consider your day-to-day experience of your home planet, the earth. You’ve
seen the sun ‘‘rise’’ and ‘‘set’’ even though you know that the sun is sitting out
there in the center of the solar system as decisively as ever. You can appreciate
why it was such an extraordinary feat of courage for Christopher Columbus
and other voyagers to deny the obvious illusion that the earth was flat and sail
off toward one of its apparent edges. Similarly, when a full moon is overhead, it
seems to follow you wherever you go even though you know the moon isn’t
chasing you. What you are experiencing is an illusion created by the great dis-
tance of the moon from your eye. When they reach the earth, the moon’s light
rays are essentially parallel and perpendicular to your direction of travel, no
matter where you go.
People can control illusions to achieve desired effects. Architects and interior
designers use principles of perception to create objects in space that seem larger
or smaller than they really are. A small apartment becomes more spacious when
it is painted with light colors and sparsely furnished with low, small couches,
chairs, and tables in the center of the room instead of against the walls. Psy-
chologists working with NASA in the U.S. space program have researched the
effects of environment on perception in order to design space capsules that
have pleasant sensory qualities. Set and lighting directors of movies and theat-
rical productions purposely create illusions on film and on stage.
Despite all of these illusions—some more useful than others—you generally
do pretty well getting around the environment. That is why researchers typi-
cally study illusions to help explain why perception ordinarily works so well.
The illusions themselves suggest, however, that your perceptual systems cannot
perfectly carry out the task of recovering the distal stimulus from the proximal
stimulus.
Approaches to the Study of Perception
You now are acquainted with some of the major questions of perception: How
does the perceptual system recover the structure of the environment? How is
ambiguity resolved? Why do illusions arise? Before we move on to answer
these questions, we need to give you more of a background in the types of
theories that have dominated research on perception.
Many of the differences between these theories can be captured by the dis-
tinction betweennatureandnurture. At issue is how much of a head start you
have in dealing with the perceptual world by virtue of your possession of the
human genotype. Do you, as anativistmight argue, come into the world with
some types of innate knowledge or brain structures that aid your interpretation
of the environment? Or do you, as anempiricistmight assert, come into the
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