Coding of Species-Specific Vocalizations by the Squirrel Monkey Auditory Cortex

Abstract

Single neurons in the auditory cortex of squirrel monkeys (Saimiri sciureus) were tested with tape-recorded vocalizations representing this species' six major call groups. A small minority of these cells were highly selective, responding only to one or two call types. For these cells, a role in categorizing discrete call types appears likely. Some selective cells behaved as “tuned filters,” by virtue of the correlation between the best frequency of steady tone bursts for a cell and the major acoustic energy in the effective call type. Most of the neurons responded to several vocalizations. A simple scheme of “feature extraction” does not appear to explain readily the responses of these cells: (a) calls effective for a given cell usually represented structurally different call groups and did not share the same simple acoustic features; (b) many cells responding across call group boundaries did not respond to all the calls of an effective call group; (c) while most of the neurons responded to steady tone bursts, their responses to tones were generally not satisfactory indicators of their responsiveness to vocalizations; (d) in some cases, the nature of a cell's response was shown to depend upon interactions of nonadjacent parts of a vocalization.