First published in 1978. Since World War II the field of perception has developed in two major directions. The first evolved out of the traditional psychophysical approach and is manifest today in the new psychophysics. The second direction is in the increasing bond between the fields of perception and cognition. This volume grew out of the context of this second direction, a particular product of two workshops (held in the Spring of 1974 and 1975), organized by the Committee on Cognitive Research of the Social Science Research Council. The Committee on Cognition was organized in 1971 to encourage communication and interaction on specific problems in the area of cognition among the various social sciences.