NSF Award
0137567
This goal of this research is to examine the relation between perceived distance and physical distance, and also to determine the way in which perceived size is related to perceived distance over distances ranging from about one meter to optical infinity. Thus, the research will deal with size and distance of terrestrial objects, as well as celestial objects, such as the moon. One particular objective is to determine if the moon illusion is a special case of ordinary size perception, or if it must be treated as a special process. It is known that people can match the physical size of an object at one distance to that of another at a much greater distance, even though their images on the retina differ dramatically in size. The ability to match physical sizes regardless of distance (size constancy) entails processing distance information. In classic theories, the perceived size of an object does not depend upon its physical distance, but upon its perceived distance. If distance is misperceived, as may occur under conditions of limited visibility, then size is also misperceived. Some cues operate over large distances, while others play a dominant role at close distances. How different cues interact with each other to influence size perception is not well understood. For this reason, some have questioned whether perceived size really depends upon perceived distance, as in the classic view. This alternative view arose in connection with theories of the moon illusion. In this alternative view, the perceived distance to the moon depends upon its perceived size, which is opposite to the classic view and has important implications for size and distance perception in general. This research will measure how well people can discriminate small differences in depth (or size) between objects over a wide range of distances out-of-doors and in a darkened laboratory containing an artificial "terrain." A small depth between two nearby objects is more easily detected than the same depth between distant objects. To be detected, the depth must be made larger with distance. Thus, since ability to discriminate depth (and differences in size) is affected by available cues to distance, manipulation of these cues will allow for examination of their effects. These studies will determine if size judgments are contingent upon capacity to discriminate differences in distance. These results will enhance our understanding of a number of tasks that are important in society in which size and distance need to be judged simultaneously. These include visual guidance of aircraft landings and similar vehicular control tasks. They will be relevant to the design of apparatus such as flight simulators.
