Speaker
Description
Norms are central to human cognition and interaction, shaping how we communicate and coordinate. Language, in particular, is governed by socially shared expectations about how and when to speak. However, the evolutionary origins of such communicative norms remain poorly understood, as protonormative behaviors in non-human primate communication are rarely documented. Vocal accommodation in the highly social and vocal common marmoset (Callithrix jacchus), where individuals modify their call structure to resemble that of their social partners, is a promising candidate for such a communicative norm. While this phenomenon is widespread among marmosets and may represent a precursor to the more advanced vocal learning essential for language, little is known about whether and how it is socially regulated. Using a closed-loop playback design based on the species’ natural vocal turn-taking, we tested twenty individuals in three interactive conditions: responses to (1) their partner’s natural calls, (2) partner-like synthetic calls gradually shifting toward their own call structure (convergence), and (3) partner-like synthetic calls gradually shifting away from it (divergence). Marmosets responded most frequently to converging calls and least to diverging ones. Diverging calls also consistently elicited agonistic tsik calls, indicating social disapproval. Crucially, tsik responses were sensitive to the direction of vocal change rather than absolute vocal similarity, suggesting active tracking of changes in partners’ calls. These findings suggest that vocal accommodation in marmosets is a socially regulated phenomenon with normative properties, offering a potential precursor to communicative norms observed in human language, with implications for the cognitive underpinnings of normativity in communication.
