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| well as striking. They illustrate,that there are both large areas of similarity among all people and important individual differences between them. The detailed understanding of these sense organs and the nervous system involves many disciplines and therefore requires explanatory exhibits on physics, neurophysiology, chemistry, and biology. Furthermore, much of technology has served to amplify and extend the domain of the senses and is therefore encompassed within a rationale that is based on perception. Perception also provides an extremely natural way of linking art and science since both of these influence the way in which people perceive their environment. Our planning includes not only the display of works by artists but also a history of perspective in painting, the cultural differences in the way European and Chinese perspective has developed, and the interesting studies on the different ways in which people who have lived only in round thatched houses react to our familiar line drawings such as the arrow length illusions. The Exploratorium has some material based on the sense of touch, on hearing, on rhythm, on balance, and on smell, but our initial development has provided more material connected with vision, optics, and the visual arts than with the other senses and arts. Our treatment of perceptual phenomena makes for a basically humanistic atmosphere in the Exploratorium, and it has, at the same time, tied together an extremely wide range of natural and technical phenomena. We feel no compulsion to “cover the ground,” nor are there narrow limits as to what is appropriate within this integrative rationale. The Exploratorium is only two years old, and much remains to be done. We are, however, encouraged by what this rationale has enabled us to accomplish thus far. The study of the mechanisms of perception is uniquely appropriate for a science museum in a way that we did not initially appreciate. There is no unique description of the way we perceive reality through our senses and there | is no easy categorization of the methodology of science. However, a statement in R. L. Gregory’s book The Intelligent Eye does suggest a parallel between the two. He states that perception “makes remarkably efficient use of strictly inadequate and so ambiguous information for selecting internally stored hypotheses of the current state of the external world.” Gregory is undoubtedly correct in his general conclusion that visual perception is not a simple stimulus-response mechanism. In his view, there are a number of possibilities for the state of the external world, one of which appears most plausibly consistent with the visual evidence. So called “illusions” reflect the normal, logical, and experiential function of the sensory mechanisms, and indeed, they would not be called illusions if we were actually deluded. They are intriguing only after one has sought out enough additional cues to determine the true nature of reality. Illusion can result from over reliance on a single cue or from an unwillingness to insist that all the evidence be consistent with the same hypothesis. The difficulty of determining the truth can result from a remarkable property of the mechanisms of perception: even in very simple situations, perceptual evidence is arranged in a strict and automatic hierarchy of importance and reliability. One tends to pay attention only to the single type of evidence that dominates this hierarchy. People require training, perhaps education, to become aware of hierarchical bias and to seek out additional kinds of evidence. Hierarchical phenomena can be illustrated in extremely simple visual situations such as a determination of the relative distance of two objects. Apparent size, color, brightness, stereoscopic evidence, and obscuration can affect this determination. If all the cues are present, even though some are arranged to be contradictory, one automatically pays attention only to the evidence at the top of the hierarchy; for example, the fact that a nearer object partially obscures the one behind it. If one eliminates the top cue, the next one takes over even though it may indicate that a different object is nearer. It is not clear how these hierarchies are established, and their order | ||