Breaking conversational rules matters to captive gorillas: A playback experiment

Abstract

Across human cultures, conversations are regulated by temporal and social rules. The universality of conversational rules suggests possible biological bases and encourages comparisons with the communicative interactions of nonhuman animals. Unexpectedly, few studies have focused on other great apes despite evidence of proto-conversational rules in monkeys, thus preventing researchers from drawing conclusions on potential evolutionary origins of this behaviour. A previous study showed however that western lowland gorillas engage in soft call interactions that seem temporally-and socially-ruled. Indeed, interactions occurred mainly between individuals close in age who followed a preset response delay, thus preventing call overlap. Here, we experimentally investigated the presence of these rules in a captive gorilla group, using a violation-of-expectation paradigm. Head orientation responses suggest that the respect of response delay matters to subjects, but the importance of the interlocutors' age proximity appeared less clear. The intensity of the response varied with subjects' age in a context-dependent way, supporting a possible role of learning. Our findings support the growing number of studies highlighting the importance of vocal turn-taking in animals and a possible sociogenesis of this ability. The capacity to "converse" might have been a key step in the co-evolution of communication and complex sociality. Despite the diversity of human cultures, some basic conversational rules are respected in all societies and thus appear universal 1. These features are gathered in a so-called "contract of communication" that conversing interlocutors informally agree on 2. The contract takes into account "context relevance" (i.e. the evaluation of the context as pertinent or not to initiate a conversation), "reciprocity" (i.e. the evaluation of both partners as valid interlocutors), and "contract-based temporal rules" (i.e. the respect of a reciprocal exchange of alternating, short, and flexible turns between two or more interlocutors 3 , and speech overlap avoidance). Several authors have questioned the possible biological bases of these conversational rules and have, for several decades, conducted cross-species comparisons to understand their origin and role across animal communication systems 4-7. To facilitate cross species investigations, authors typically distinguish "conversation-like vocal exchanges" from other vocal patterns like isolated calling (one call emitted and no other calls can be heard around, e.g. in red-capped mangabeys Cercocebus torquatus 8), repeated calling (the same caller calls several times in a row, e.g. in Japanese macaques Macaca fuscata 9), disorganized phonoresponses (one individual produces a call, typically an alarm call that triggers calls in an apparent chaotic way from the other group members, e.g. in blue monkeys Cercopithecus mitis stuhlmanni 10), chorusing (two or more individuals overlap their emission of a given call type, e.g. in chimpanzees Pan troglodytes 11) and duetting (two...

Why study turn‐taking sequences in interspecies interactions?

“…Essentially, human conversation serves as a matrix for understanding the distribution of vocal communication between individual animals. Such rule-governed organizational properties have been reported in the vocal interactions of primates (Masataka, 2003), meerkats (Demartsev et al, 2018), bonobos (Levrero et al, 2019, and gorillas (Pougnault et al, 2020), as well as in birds (Henry et al, 2015). In particular, 9 these studies report phenomena of overlap avoidance and interlocutor selectivity rules (Levrero et al, 2019).…”

“…Although counter‐intuitively (for it only dealt with the properties of human unique capacity of articulate verbal language), this notion has recently been brought, and appropriated, by the field of animal communication. The existence of rule‐governed conversation‐like mechanisms has since been investigated in a vast array of animal species: in birds and nonhuman primates, of course, but also in many mammals such as elephants, whales, dolphins and bats (see Pougnault, 2020).…”

Turn-taking skills in mammals: A systematic review into development and acquisition

“…Here, we considered only those studies that involved individuals observing and reacting to turn-taking interactions of other interactants. Miller et al, 2004;Méndez-Cárdenas and Zimmermann, 2009;Morisaka et al, 2013;Terleph et al, 2018; see Figure 1), the field is strongly biased toward investigations involving primates (e.g., Rossano, 2013;Takahashi et al, 2013;Fröhlich et al, 2016c;Snowdon, 2017;Pougnault et al, 2020). Furthermore, Vanderhoff and Bernal Hoverud (2022) recently provided an overview of communicative exchanges in non-primate mammals with a special focus on antiphonal calling, duetting, and counter-singing (for definitions of terms, see Box 1) and showed that some singing species also possess turn-taking abilities.…”

“…Number of studies indexed in the Scopus and Web of Science databases that included the terms "duet" or "turn-taking" or "antiphonal calling" combined with the words "animal" or "non-human" or "Animalia" or "fauna" across years ( -). Overall, specific temporal relationships in turn-taking interactions have been found in a variety of non-mammal taxa including amphibians, birds, and insects (see for a recent review Pika et al, 2018;Pougnault et al, 2020;de Reus et al, 2021). Pika et al (2018), however, concluded that considerable methodological confounds and the employment of different terminologies in the existing studies (e.g., antiphonal calling and duetting) have significantly hampered insightful comparisons across species and an in-depth understanding of turn-taking complexity.…”

Social pressure drives “conversational rules” in great apes

“…it is rarely shorter than the mean duration of a call, although most published maximum response delays appear slightly shorter in monkeys (around 1 or 1.5 s). Recent playback experiments using violation‐of‐expectations on gorillas and bonobos revealed that individuals could perceive whether a short silent gap between vocalisations produced by different interlocutors is present (Levréro et al ., 2017; Pougnault et al ., 2020). These results suggest that the presence of a response delay matters to the audience (Levréro et al ., 2017; Pougnault et al ., 2020).…”