This research will study the perceptual and cognitive processes involved in the identification and categorization of sets of visual stimuli that vary on two or more physical dimensions. The research is motivated by decision-bound theory, which assumes there is variability in the perceptual information associated with repeated presentations of every object or event. The theory assumes that the perceptual information obtained from any one presentation can be described by a set of coordinate values along each of the relevant perceptual dimensions. When learning to identify unfamiliar objects or events or when learning new categories, humans are assumed to construct decision boundaries that partition the perceptual space into regions. Each region is associated with an object or event name or with the name of a category. When a new object is encountered, the person determines in which region the percept has fallen and then identifies or categorizes the object by the name associated with that region. This research will consist of four projects. The first will measure the distribution of information available in a visually- presented stimulus along the experimenter-defined stimulus dimensions. The second will test for possible interactions between different functional units in the visual cortex. When incorporated into decision-bound theory, the results of these two projects might be used to construct machines that identify or categorize visual stimuli as well as do humans. The third project will study how humans learn categories, by focusing on a number of alternative descriptions of how category boundaries are learned. The final project will study the time it takes humans to make categorization judgments. In particular, the project will try to elucidate the relation between response time and the positioning of the stimulus representation in perceptual space and, specifically, on its relation to the exemplars of contrasting categories. This knowledge will increase our understanding of how children learn to read and name objects in their environment.
