The proposed research seeks to determine whether nonhuman primates engage a categorical mode of processing when listening to species-specific vocalizations. Field-recorded vocalizations of the Japanese macaque (Macaca fuscata) will be used as models for the construction of synthetic acoustic continua between acoustically- and sociobehaviorally-related communication sounds. Two separate continua will be generated--one between a pair of vocalizations distinguished by the relative temporal position of a specific acoustic cue within the sounds and a second between a pair of calls differentiated by their relative rise time values at stimulus onset. Japanese macaques and either stumptailed macaques (M. arctoides) or vervets (Cercopithecus aethiops) will be tested, via operant conditioning techniques, for their ability 1) to classify individual exemplars from the separate continua as belonging to one of two categories and 2) to discriminate between pairs of sounds separated by varying physical acoustic distances along each of the continua. The primary dependent variables in the classification task will be percent classification (e.g., class 1 vs. class 2) and reaction time. The primary dependent variables in the discrimination task will be percent correct, from which differential acuity indices (i.e., difference limens) will be calculated, and reaction time. The independent variables will be the two different stimulus continua and the species of the animal listeners. Additional, selective adaptation experiments are planned should either of the continua be categorically perceived in order to elucidate the probable neural character of the auditory property analyzers underlying this categorical processing mode. The data of principal interest in these followup experiments will be: 1) the location of category boundaries determined in the classification paradigm; and 2) the loci of regions of best discriminability determined in a discrimination task.