The present proposal aims to understand the relationship between hearing, vocal development, and vocal learning in a small Australian parrot, the budgerigar with comparisons to more familiar songbird models. Budgerigars learn new vocalizations throughout life, and for a number of reasons, provide a better animal model for studying some biological processes underlying human speech and language earning than the better studied songbirds. The present proposal involves both psychophysical and physiological approaches to the study of hearing, perception, the production of vocal signals in budgerigars with comparisons to other species. The present proposal also brings vocal learning under operant control in an animal model providing a new range of opportunities to explore the relation between auditory perception and vocal production. Past work has revealed several ways in which the bird auditory system functions in a way that is dramatically different from what we know of mammalian auditory function. In some cases, this enhanced discrimination ability appears to be related to the nature of species-specific vocal signals. The comparative approach is particularly effective at revealing these areas of interest. In this proposal we also propose to use operant control of vocal behavior and small earphones to examine, in fine detail, the characteristics of the audio-vocal circuit in budgerigars that maintains a normal, learned vocal repertoire. Attempts will be made to extend these techniques to the more familiar songbird species using their calls rather than songs. The goal is to characterize the acoustic production and perception system in an animal model that shares with humans a plasticity that extends throughout adulthood.