Sound spectral properties of conditioned vocalization in monkeys

Four monkeys were trained to emit vocalizations which were analyzed with a sound spectrograph and swept frequency analyzer. Over the course of the study, the monkeys increased the duration of their calls and changed the character of the calls by the elimination of noise and high frequency harmonics. At the end of training, the calls emitted by the four monkeys were similar to each other in frequency composition, and there was consistency of vocal format among successive calls given by an individual monkey. It is suggested that nonhuman primates be utilized for the further study of mechanisms of phonation.