The goal of our program is the understanding of how the vertebrate auditory nervous system processes species-specific vocal signals. This research will focus on both the neural basis of recognition of these signals as well as the underlying mechanisms that enable their spatial localization. Our approach is based primarily on our previous neurobehavioral studies of anurans (frogs and toads) spanning the past many years. Since we have found that the peripheral and central auditory nervous system of different species is selectively tuned to detect certain signal features in their species-specific advertisement calls, we wish to continue to explore the transformations at various levels of their auditory system which give rise to the selectivity. We also will begin studies of neural encoding of the other calls in their vocal repertoire to determine if there are separate channels for processing these other important sounds. Recordings from single neurons will be conducted in the eighth nerve, brainstem nuclei, and in the forebrain of anesthetized animals in response to a variety of acoustic stimuli including natural and synthetic vocal signals. From a recent behavioral study we have evidence that anurans rely on a pressure gradient mechanism involving sound coupling through their Eustachian tubes to their bilateral middle ear cavities in order to achieve accurate sound localization. In a collaborative study we will employ laser vibrometry to characterize the biophysical principles involved in this novel scheme. We believe that the results of our overall research program will provide needed insight into similar questions of sensory processing of vocal signals in higher vertebrates but which are much more difficult to unravel. We are convinced that studies of lower, simpler vocal vertebrates serve as valuable models for understanding the fundamental processes that have given rise to hearing and speech recognition in the human auditory nervous system.
