On the Vocal Expression of Emotion. A Multi-Parametric Analysis of Different States of Aversion in the Squirrel Monkey

There is general agreement that in non-human primates, the emotional state of a caller is reflected in the vocal structure. But only few studies describe call features characterizing such correlates. This is mainly due to the fact that it is difficult to identify the emotional state of a caller. In the present study, we analysed calls from a study (Jürgens, 1979) in which squirrel monkeys had been given the opportunity to control vocalization-eliciting brain stimulation. In this way, the aversive or hedonistic quality of the emotional state underlying the production of specific calls could be determined. 758 of the recorded calls, representing 8 different call types, given by 25 subjects, were analysed in order to find out whether differences in the degree of aversion are reflected by specific acoustic parameters. It was found that an increase in aversion is parallelled, depending upon the call type, by an upward shift of maximal energy in the power spectrum, an increase in frequency range and/or an increase in the ratio of nonharmonic to harmonic energy.