Abstract
As studies in echo-locating bat have taught us how the brain processes sonar signals, our understanding of cortical processing of communication sounds in nonhuman primate models can provide invaluable insights into brain mechanisms underlying perception of speech or speech-like signals. I’ll discuss recent work from my laboratory in a vocal primate, common marmoset, in which we quantitatively analyzed their species-specific vocalizations and systematically studied corresponding cortical responses. Our study revealed that marmoset vocalizations are highly complex but well structured and contains precise information for the recognition of call types as well as caller identity in a finite-dimensional space. The characteristics of marmoset vocalizations suggests that cortical representations of these sounds are unlikely to be based on “call-detectors”. In our neurophysiological experiments conducted in awake marmosets, we have studied cortical responses to various types of marmoset vocalizations in populations of single neurons in both the primary and secondary auditory cortex. Quantitative techniques were used to synthesize and alter natural vocalizations in order to test sensitivity of cortical neurons to perturbations along important stimulus dimensions. Our results indicate that cortical representations of spectrally and temporally complex vocalizations are based on distributed, partially overlapping neuronal populations, and that the behavioral relevance of these sounds plays an important role in shaping neural responses in the auditory cortex. Taken together, these findings illustrate the importance of studying cortical functions in an appropriate experimental model in order to understand brain mechanisms underlying perception of species-specific communication sounds.