Active Sampling in Primate Vocal Interactions

Active sensing is a behavioral strategy for exploring the environment. In this study, we show that contact vocal behaviors can be an active sensing mechanism that uses sampling to gain information about the social environment, in particular, the vocal behavior of others. With a focus on the real-time vocal interactions of marmoset monkeys, we contrast active sampling to a vocal accommodation framework in which vocalizations are adjusted simply to maximize responses. We conducted simulations of a vocal accommodation and an active sampling policy and compared them with real vocal exchange data. Our findings support active sampling as the best model for marmoset monkey vocal exchanges. In some cases, the active sampling model was even able to predict the distribution of vocal durations for individuals. These results suggest a new function for primate vocal interactions in which they are used by animals to seek information from social environments. SignificanceWe found that marmoset monkeys use vocal exchanges with conspecifics in the same way that bats and electric fish use their self-generated signals: to sample the information space. The difference is that, while bats, electric fish and other echolocating animals emit signals and then interpret that signals reflection, for vocalizing marmoset monkeys the "reflection" is the vocal response from conspecifics. We show that marmosets produce variable vocalizations as a means to sample the acoustic space in which they can elicit a conspecific response. They are actively sampling--learning about their dyadic partner like a bat learns about its prey.