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Abstract

The vocal behavior of macaque monkeys has been studied extensively in both field and laboratory settings. To date, however, no investigation has systematically examined the neural mechanisms underlying species-specific recognition of their vocalizations. To bridge this gap, we are investigating the auditory representation of conspecific vocalizations in the neocortex of behaving rhesus monkeys. Subjects performed a simple auditory detection task during which, on each trial, they listened to a conspecific vocalization followed by a non-vocal, target sound. The stimulus set consisted of call types familiar to our captive-bred subjects but from unknown individuals: three exemplars from each of 7 call categories. Our preliminary investigation using these natural stimuli (Ghazanfar et al, SFN 2002) revealed that ~45 of auditory belt cortical multi-units were selective for 1 or 2 call categories. This suggests that the macaque auditory cortex is specialized to process communication sounds. To assess the degree of this specialization and the specificity of vocalization-sensitivity, we are comparing single-unit responses to vocalizations with time-reversed versions, pure-tones and band-passed noise. For each vocalization, a pure-tone and a band-passed noise stimulus were generated to match the signal’s duration, dominant frequency and average RMS power. Recordings from both core and belt cortical areas will determine whether vocalization-sensitive neurons in these regions are driven by simple features of the signal or by more complex interactions between spectral and temporal properties.