Page 202 - Foundations of Cognitive Psychology : Core Readings

206 Stephen E. Palmer

Figure 8.15
Effects of past experience on grouping. Once you se the Dalmatian in the center, it will forever
change the grouping you perceive when viewing this picture. This change can only be attributed to
past experience, which can have a dramatic effect on perceived organization of ambiguous images.
(Photography by R. C. James.)

situations. Figure 8.15 illustrates the point. Initially, you will probably see this
picture as a nearly random array of black regions on a white background. Once
you are able to see it as a Dalmatian with its head down, sniffing along a street,
the picture becomes dramatically reorganized with certain of the dots going
together because they are part of the dog and others going together because
they are part of the street. The interesting fact is that once you have seen the
Dalmatian in this picture, you will continue to see it that way for the rest of
your life. Past experience can thus have a dramatic effect on grouping and or-
ganization, especially if the organization of the image is highly ambiguous.
The principle of past experience is fundamentally different from the other
factors Wertheimer discussed in that it concerns not geometrical properties of
the stimulus configuration itself, but rather the viewer’s history with respect
to the configuration. Perhaps partly for this reason, it has largely been ignored
in subsequent presentations of Gestalt principles of grouping. Another reason
may be that it is rather easy to show that other grouping factors can block rec-
ognition of even the most frequently seen objects (e.g., Gottschaldt, 1929). Fig-
ure8.16shows an exampleinwhich theverysimple, common shapeofa
rectangular prism (figure 8.16A) is completely hidden in a configuration (figure
8.16B) in which good continuation, symmetry, and other intrinsic factors make
the embedded prism nearly impossible to perceive. In fairness to past experi-
ence, it is important to realize that, unlike the Dalmatian example, in which the