inferences (reasonable hunches) about the general class of objects or events that
the images might represent. Since this process takes place out of your conscious
awareness, Helmholtz termed itunconscious inference.Ordinarily, these infer-
ential processes work well. However, perceptual illusions can result when
unusual circumstances allow multiple interpretations of the same stimulus or
favor an old, familiar interpretation when a new one is required.
Helmholtz’s theory broke perception down into two stages. In the first,ana-
lyticstage, the sense organs analyze the physical world into fundamental sen-
sations. In the second, syntheticstage, you integrate and synthesize these
sensory elements into perceptions of objects and their properties. Helmholtz’s
theory proposes that you learn how to interpret sensations on the basis of your
experience with the world. Your interpretations are, in effect, informed guesses
about your perceptions.
The Gestalt Approach Gestalt psychology,founded in Germany in the second
decade of the twentieth century, put greater emphasis on the role of innate
structures—nature—in perceptual experience. The main exponents of Gestalt
psychology, likeKurt Koffka(1935),Wolfgang Ko ̈hler(1947), andMax Wertheimer
(1923), maintained that psychological phenomena could be understood only
when viewed as organized, structuredwholesand not when broken down
into primitive perceptual elements. The termGestaltroughly means ‘‘form,’’
‘‘whole,’’ ‘‘configuration,’’ or ‘‘essence.’’ Gestalt psychology challenged atom-
istic views of psychology by arguing that the whole is more than the sum of its
parts. For example, when you listen to music, you perceive whole melodies
even though they are composed of separate notes. Gestalt psychologists argued
Figure 7.8
The Hermann grid. Two ganglion-cell receptive fields are projected on this grid; it is an example of
an illusion at the sensory stage.
146 Philip G. Zimbardo and Richard J. Gerrig