SBBC continues to focus on the vocal behavior of nonhuman primates, using the squirrel monkey as a model for basic and universal truisms of language. Ape and monkey vocal communication has traditionally been seen as highly programmed genetically and closed to learning, in contrast to the acquisition of language skills by human infants or even by birds. Early work in European labs indicated that, for the squirrel monkey, vocal production is at birth equivalent to that of adults. However, our data recently collected from 6 infant subjects over the first year of life, indicate that developmental changes clearly do occur, although certainly not of the magnitude of human language acquisition. Behavioral data collected along with the production data have revealed that it is aunts (female relatives or unrelated friends of the mother) and not the mothers themselves who interact vocally most often with very young infants, and that it is aunts who elicit the first vocal responses. Among adult squirrel monkeys, the exchange of chuck vocalizations has been shown by this laboratory to have many of the characteristics of human conversation. Using a technique of recording animals' voices and then playing them back, this past year we showed that females responded significantly more often to the chucks of group members than to those of strangers. We are currently testing the ability of females to discriminate a very sophisticated (for primates) and acoustically subtle (for humans) distinction between chucks uttered either first or second in a dialogue, a sequence which has informational properties comparable to a question and answer.
