what else you see around you, your identification may vary. Read the follow-
ing words:
They sayTHE CAT, right? Now look again at the middle letter of each word.
Physically, these two letters are exactly the same, yet you perceived the first as
an H and the second as an A. Why? Clearly, your perception was affected by
what you know about words in English. The context provided by T_E makes an
H highly likely and an A unlikely, whereas the reverse is true of the context of
C_T (Selfridge, 1955).
Researchers have often documented the effects of context and expectation on
your perception (and response) by studying set.Setis a temporary readiness
to perceive or react to a stimulus in a particular way. There are three types of
set: motor, mental, and perceptual. Amotor setisareadinesstomakeaquick,
prepared response. A runner trains by perfecting a motor set to come out of
the blocks as fast as possible at the sound of the starting gun. Amental setis a
readiness to deal with a situation, such as a problem-solving task or a game, in
a way determined by learned rules, instructions, expectations, or habitual ten-
dencies. A mental set can actually prevent you from solving a problem when
the old rules don’t seem to fit the new situation. Aperceptual setis a readiness
to detect a particular stimulus in a given context. A new mother, for example, is
perceptually set to hear the cries of her child.
Often a set leads you to change your interpretation of an ambiguous stimu-
lus. Consider these two series of words:
FOX; OWL; SNAKE; TURKEY; SWAN; D?CK
BOB; RAY; DAVE; BILL; HENRY; D?CK
Did you read through the lists? What word came to mind for D? CK in each
case?IfyouthoughtDUCKandDICK,it’sbecausethelistofwordscreateda
setthatdirectedyoursearchofmemoryinaparticularway.
Labels can provide a context that gives a perceptual set for an ambiguous
figure. You have seen how meaningless droodles turn into meaningful objects.
Look carefully at the picture of the woman in figure 7.40A; have a friend (but
not you) examine figure 7.40B. Next, together look at figure 7.40C—what does
each of you see? Did the prior exposure to the unambiguous pictures with their
labels have any effect on perception of the ambiguous image? This demonstra-
tion shows how easy it is for people to develop different views of the same
person or object, based on prior conditions that create different sets.
All the effects of context on perception clearly require that your memory be
organized in such a fashion that information relevant to particular situations
becomes available at the right times. In other words, to generate appropriate
(or inappropriate) expectations, you must be able to make use of prior knowl-
edge stored in memory. Sometimes you ‘‘see’’ with your memory as much as
you see with your eyes.
182 Philip G. Zimbardo and Richard J. Gerrig