Hockenbury Discovering Psychology 5th txtbk

126 CHAPTER 3 Sensation and PerceptionAn Impossible Figure: Escher’s Waterfall(1961) Impossible figures are visual riddlesthat capitalize on our urge to organize visualelements into a meaningful whole.Though not illusions in the true sense,these figures baffle our natural tendencyto perceptually organize a scene(Ramachandran & Rogers- Ramachandran,2007). Dutch artist M. C. Escher(1898–1972) became famous for creatingelaborate impossible figures, using perceptualprinciples to create complex visualpuzzles. In most paintings, depth and distancecues are used to produce realisticscenes. But in Escher’s work, the depthcues are often incompatible, producing aperceptual paradox. As you try to integratethe various perceptual cues in thedrawing into a stable, integrated whole,you confront perceptual contradictions—such as the conclusion that water is runninguphill. Escher was fascinated by the“psychological tension” created by suchimages (Schattschneider, 1990).If you look at a full moon on the horizon through a cardboard tube, you’llremove the distance cues provided by the horizon. The moon on the horizonshrinks immediately—and looks the same size as it does when directly overhead.What Is The Hidden Shape?(a)(b)Figure 3.20 Which Tabletop Is Longer?The Shepard Tables illusion consists of twotables that are oriented in different directions.It capitalizes on our automatic useof depth perception cues to perceive whatis really a two-dimensional drawing asthree-dimensional objects. By relying onthese well-learned depth perception cues,most people pick (a) as being the longertabletop. In contrast, Mike May was obliviousto the perceptual illusion. He correctlyresponded that the two tabletops werethe same size and shape (Fine & others,2003). You can verify this with a ruler.Source: Illusion adapted from Shepard (1990).Mike and Perceptual IllusionsPerceptual illusions underscore the fact that what we see is not merely a simple reflectionof the world, but our subjective perceptual interpretation of it. We’ve beendeveloping and refining our perceptual interpretations from infancy onward. Butwhat about Mike, who regained low vision after more than four decades of blindness?Psychologist Ione Fine and her colleagues (2003) assessed Mike’s perceptualprocessing with a couple of perceptual illusions. For example, Mike was presentedwith an image containing illusory contours, shown above left. It’s much like themore complex image we discussed in Figure 3.18. When asked, “What is the ‘hidden’shape outlined by the black apertures?” Mike had no response. However, whenthe form was outlined in red, Mike immediately perceived the red square.Now look at Figure 3.20 shown in the margin. Which tabletop is longer? If you usedyour keen perceptual skills and confidently said (a), you’re wrong. If you responded asMike did and said that the two tabletops are of identical size and shape, you’d be correct.You can use a ruler or tracing paper to verify this. This illusion is referred as theShepard Tables, named after its creator, psychologist Roger Shepard (1990).Why wasn’t Mike susceptible to this compelling visual illusion? Partly, it’sbecause he does not automatically use many of the depth perception cues we discussedearlier (Gregory, 2003). As psychologist Donald MacLeod explained, “Mikeis impressively free from some illusions that beset normal vision, illusions that reflectthe constructive processes involved in the perception of three-dimensional objects”(Abrams, 2002).Although seeing is said to be believing, in the case of illusions, believing can leadto seeing something that isn’t really there. As Mike gets more perceptual practicewith the world, it will be interesting to see if he learns to fall for the same illusionsthat most of us do.Like any psychological process, perception can be influenced by many factors,including our expectations. In the final section of this chapter, we’ll consider howprior experiences and cultural factors can influence our perceptions of reality.