Page 244 - Understanding Psychology

Figure 8.18 Lines of Different Lengths?
The Müller-Lyer illusion (a) and the Ponzo illusion (b) are depicted here. The lines between the arrowheads in (a) are exactly the same length, as are the heavy black lines in (b). Some psychologists believe that the reason the lines in (a) seem of different lengths is because they are interpreted as offering different cues to their distance from the viewer. The lines in (b) may appear to be different in length because the brain interprets this diagram as though it is from a scene such as that in (c). Why does the brain interpret scenes in certain ways?
c
a
b
extrasensory perception (ESP): an ability to gain infor- mation by some means other than the ordinary senses
each set are longer? Measure the lengths of the pairs of lines with a ruler, then look again. Do the lines look as long now that you know they are the same? For most people, the answer is no.
A possible explanation of this type of illusion is that even though the patterns are two-dimensional, your brain treats them as three- dimensional. These illusions have features that usually indicate distance in three- dimensional space. The top line in Figure 8.18a, for example, can be thought of as the far corner of a room; the bottom line is like the near corner of the building. In Figure 8.18b and Figure 8.18c, the converging lines create the illusion of dis- tance so that the lower bar looks nearer and shorter
than the upper bar. This perceptual compensation seems to be uncon- scious and automatic.
Figure 8.19 shows two individuals in a room. Their sizes look dra- matically different because you perceive the room as rectangular. In fact, the ceiling and walls are slanted so that the back wall is both shorter and closer on the right than on the left. Yet even when you know how this illusion was achieved, you still accept the peculiar difference in the sizes of the two people because the windows, walls, and ceiling appear rectan- gular. Your experience with rectangular rooms overrides your knowledge of how this trick is done.
EXTRASENSORY PERCEPTION
We are fascinated by things that cannot be seen, easily explained, or sometimes even verified, such as flying saucers, atoms, genes, and extrasensory perception. Extrasensory perception (ESP)—receiving information about the world through channels other than the normal senses—is a hotly debated topic. There are four types of ESP: (1) clairvoy- ance is perceiving objects or information without sensory input; (2) telepa- thy involves reading someone else’s mind or transferring one’s thoughts; 3) psychokinesis involves moving objects through purely mental effort;
230 Chapter 8 / Sensation and Perception