UC San Diego

Complex social behaviors are at the heart of primate societies. Abiding by social rules that govern these behaviors is a critical part of the life of a social primate. In communication, social rules exist to regulate if, when, and what an individual vocalizes, as well as how a receiver responds. These rules are crucial to the efficacy of social communication systems. But what happens when individuals stop following these rules? Here, I investigated the consequences of rule-breaking during communication in common marmosets (Callithrix jacchus). I utilized one of their natural rule-governed behaviors known as antiphonal calling, which involves a back and forth exchange of calls between conspecifics. Rules guiding this vocal behavior include a high level of reciprocity, short response latencies, and turn-taking with minimal interrupting. This dissertation examines how captive marmosets respond to individuals breaking vs. following these rules. I created a novel interactive playback environment where subjects communicated with two marmosets called Virtual Monkeys (VMs). Each VM was a speaker that represented an individual by broadcasting prerecorded calls from a single marmoset. In Chapter 1, I manipulated timing and reciprocity rules by varying how quickly and how likely each VM was to respond when subjects vocalized. I found that subjects were biased against communicating with rule-breakers (i.e., one that responds slowly and infrequently) when a rule-follower (i.e., one that responds quickly and often) was also present. In Chapter 2, I manipulated turn-taking rules by having one VM occasionally interrupt subjects (a rule-breaker) and the second VM behave normally (a rule-follower). I found that subjects were less likely to respond to interruptions, though there was no lasting bias in communication preferences to either VM. In Chapter 3, I sought to establish a foundation for investigating auditory processes in the awake marmoset brain with functional magnetic resonance imaging. Using a battery of auditory stimuli, I found representative properties of the auditory system, including strong activation of auditory cortices, a tonotopic auditory core, and secondary regions driven by complex stimuli. This preparation can one day be used to investigate brain areas involved in processing rule violations during antiphonal calling. Taken together, this dissertation demonstrates that marmosets use flexible strategies during communication and adapt their behavior to different contexts. This likely reflects a broader social cognitive strategy for successfully navigating primate societies and the close relationship between communication and cognition in our Order.