Most investigations of auditory function described thus far come from either behavioral studies in humans or physiological investigations in animals. There is a limit to what these approaches can tell us about the coding of complex sounds. With behavioral measures of what an animal actually perceives along with physiological measures in the same animal, one can determine with certainty whether putative neural encoding strategies are relevant or not. In an effort to reconcile behavior and physiology, we have begun measuring detection thresholds for various complex stimuli in birds and mammals. Specifically, stimuli include those used in birds by Shamma and Dooling [.Shamma Dooling 1996.] to discover the multiscale cortical representations ( Thrust area I(C)), and those used with rabbits by Kidd and Carney as described in section ( Thrust area III(B)) above. Birds show values that are similar to those of humans [.Shamma Dooling 1996.], and more interestingly, preliminary data also suggest that there are single units in Field L of the bird brain that respond to these complex stimuli much like in the ferret [.Shamma rip1 1995.]. Such findings in organisms as diverse as a ferret and a bird argue for a general coding scheme for complex sounds in the vertebrate auditory system and may explain why non-human mammals and birds perceive sounds such as speech like humans do.
We plan to extend these investigations in birds, rabbits, and ferrets. For example, we have already initiated behavioral experiments in the ferret similar to those already done in bird to measure and compare their behavioral and physiological responses. We shall also complement these psychoacoustical experiments with physiological recordings in the bird. This will allow us to accumulate sufficient data for a comprehensive assessment of the behavior and physiology in these two animal models, and to compare them to those collected from human subjects.