discoveringpsych7e

The Effects of Experience on Perceptual Interpretations

Our educational, cultural, and life experiences shape what we perceive. As a simple example, consider a climbing wall in a gym. If your knowledge of climbing is limited, the posts, ropes, arrows, and lines look like a meaningless jumble of equipment. But if you are an expert climber, you see handgrips and footgrips, belays, overhangs, and routes of varying difficulty. Our different perceptions of a climbing wall are shaped by our prior learning experiences.

The $28,000 Grilled Cheese Sandwich: What Do You See? Is that Madonna on that grilled cheese sandwich? Ten years after she first noticed what she thought was the face of the Virgin Mary on her grilled cheese sandwich, Diana Duyser auctioned it off on eBay. The winning bid? Duyser got $28,000 for her carefully preserved (and partially eaten) relic. Why are we so quick to perceive human faces in ambiguous stimuli?

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Learning experiences can vary not just from person to person but also from culture to culture. The Culture and Human Behavior box on page 126, “Culture and the Müller-Lyer Illusion,” discusses the important role that unique cultural experiences can play in perception.

Perception can also be influenced by an individual’s expectations, motives, and interests. The term perceptual set refers to the tendency to perceive objects or situations from a particular frame of reference. Perceptual sets usually lead us to reasonably accurate conclusions. If they didn’t, we would develop new perceptual sets that were more accurate. But sometimes a perceptual set can lead us astray. For example, someone with an avid interest in UFOs might readily interpret unusual cloud formations as a fleet of alien spacecraft. Sightings of Bigfoot, mermaids, and the Loch Ness monster that turn out to be brown bears, manatees, or floating logs are all examples of perceptual sets.

People are especially prone to seeing faces in ambiguous stimuli, as in the photos shown on previous page. Why? One reason is that the brain is wired to be uniquely responsive to faces or face-like stimuli (Leopold & Rhodes, 2010; Pascalis & Kelly, 2009). Research by Doris Tsao and her colleagues (Tsao, 2006; Tsao & others, 2006) showed that the primate brain contains individual brain neurons that respond exclusively to faces or face-like images. This specialized face-recognition system allows us to identify an individual face out of the thousands that we can recognize (Kanwisher & Yovel, 2009).

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But this extraordinary neural sensitivity also makes us more liable to false positives, seeing faces that aren’t there. Vague or ambiguous images with face-like blotches and shadows can also trigger the brain’s face-recognition system. Thus, we see faces where they don’t exist at all—except in our own minds.

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CULTURE AND HUMAN BEHAVIOR

Culture and the Müller-Lyer Illusion: The Carpentered-World Hypothesis

Since the early 1900s, it has been known that people in industrialized societies are far more susceptible to the Müller-Lyer illusion than are people in some nonindustrialized societies (Matsumoto & Juang, 2008; Phillips, 2011). How can this difference be explained?

Cross-cultural psychologist Marshall Segall and his colleagues (1963, 1966) proposed the carpentered-world hypothesis. They suggested that people living in urban, industrialized environments have a great deal of perceptual experience in judging lines, corners, edges, and other rectangular, manufactured objects. Thus, people in carpentered cultures would be more susceptible to the Müller-Lyer illusion, which involves arrows mimicking a corner that is jutting toward or away from the perceiver.

In contrast, people who live in noncarpentered cultures more frequently encounter natural objects. In these cultures, perceptual experiences with straight lines and right angles are relatively rare. Segall predicted that people from these cultures would be less susceptible to the Müller-Lyer illusion.

A Noncarpentered Environment People who live in urban, industrialized environments have a great deal of perceptual experience with straight lines, edges, and right angles. In contrast, people who live in a noncarpentered environment, like the village shown here, have little experience with right angles and perfectly straight lines (Phillips, 2011). Are people who grow up in a noncarpentered environment equally susceptible to the Müller-Lyer illusion?

David Poole/Robert Harding Picture Library Ltd/Alamy

To test this idea, Segall and his colleagues (1963, 1966) compared the responses of people living in carpentered societies, such as Evanston, Illinois, with those of people living in noncarpentered societies, such as remote areas of Africa. The results confirmed their hypothesis. The Müller-Lyer illusion was stronger for those living in carpentered societies. Could the difference in illusion susceptibility be due to some sort of biological difference rather than a cultural difference? To address this issue, psychologist V. Mary Stewart (1973) compared groups of white and African American schoolchildren living in Evanston, Illinois. Regardless of race, all of the children living in the city were equally susceptible to the Müller-Lyer illusion. Stewart also compared groups of black African children in five different areas of Zambia—ranging from the very carpentered capital city of Lusaka to rural, noncarpentered areas of the country. Once again, the African children living in the carpentered society of Lusaka were just as susceptible to the illusion as the Evanston children, but the African children living in the noncarpentered countryside were not.

These findings provided some of the first evidence for the idea that culture could shape perception. As Segall (1994) later concluded, “Every perception is the result of an interaction between a stimulus and a perceiver shaped by prior experience.” Thus, people who grow up in very different cultures might well perceive aspects of their physical environment differently.