A stepping stone to compositionality in chimpanzee communication

Abstract

Compositionality refers to a structural property of human language, according to which the meaning of a complex expression is a function of the meaning of its parts and the way they are combined. Compositionality is a defining characteristic of all human language, spoken and signed. Comparative research into the emergence of human language aims at identifying precursors to such key features of human language in the communication of other primates. While it is known that chimpanzees, our closest relatives, produce a variety of gestures, facial expressions and vocalizations in interactions with their group members, little is known about how these signals combine simultaneously. Therefore, the aim of the current study is to investigate whether there is evidence for compositional structures in the communication of chimpanzees. We investigated two semi-wild groups of chimpanzees, with focus on their manual gestures and their combinations with facial expressions across different social contexts. If there are compositional structures in chimpanzee communication, adding a facial expression to a gesture should convey a different message than the gesture alone, a difference that we expect to be measurable by the recipient’s response. Furthermore, we expect context-dependent usage of these combinations. Based on a form-based coding procedure of the collected video footage, we identified two frequently used manual gestures (stretched arm gesture and bent arm gesture) and two facial expression (bared teeth face and funneled lip face). We analyzed whether the recipients’ response varied depending on the signaler’s usage of a given gesture + face combination and the context in which these were used. Overall, our results suggest that, in positive contexts, such as play or grooming, specific combinations had an impact on the likelihood of the occurrence of particular responses. Specifically, adding a bared teeth face to a gesture either increased the likelihood of affiliative behavior (for stretched arm gesture) or eliminated the bias toward an affiliative response (for bent arm gesture). We show for the first time that the components under study are recombinable, and that different combinations elicit different responses, a property that we refer to as componentiality. Yet our data do not suggest that the components have consistent meanings in each combination—a defining property of compositionality. We propose that the componentiality exhibited in this study represents a necessary stepping stone toward a fully evolved compositional system.

A review of research in primate sanctuaries

“…Observational studies, in which resident primates are watched from afar without any disruption to their daily routine, are classically non-invasive in nature and the scientific investment to procure these data is relatively modest. Great ape (particularly chimpanzee) behavioural studies are typically the most prevalent in sanctuary settings, with studies focusing on activity budgets [ [51][52][53] and Chimfunshi [54]. At Lola Ya Bonobo in the Democratic Republic of Congo (hereafter Lola), studies have focused on bonobos' copulation calls [55][56][57][58], gestures [59,60], vocal-gestural combinations in infants [61], sex signals [62], communication signals [63] and contest hoots [64].…”

The origins of gestures and language: history, current advances and proposed theories

“…gestures associated with vocalisations or facial expressions) to convey informative content (e.g. Crockford et al ., ; Schel et al ., ; Fischer & Price, ; Hobaiter, Byrne & Zuberbühler, ; Deshpande, Gupta & Sinha, ; Oña, Sandler & Liebal, ). In addition, very little is known about meaningful combinations or intentional use of facial expressions (Waller, Caeiro & Davila‐Ross, ; Scheider et al ., ).…”

“…Moreover, various characteristics can influence their signalling behaviour, mainly the use of different types of uni‐ or multimodal and multicomponent signalling [e.g. unimodal signal types (Ouattara, Lemasson & Zuberbühler, ; Cochet & Vauclair, ; Waller & Cherry, ); gesture sensory modality (auditory, tactile or visual) (Roberts & Roberts, ; Prieur et al ., ); gesture–vocal combinations (Hobaiter, Byrne & Zuberbühler, ; Genty, ); gesture–facial expression combinations (Oña, Sandler & Liebal, ); multicomponent combinations (e.g. visual gesture with facial expression; Micheletta et al ., ; Liebal et al ., )], signal sequence [e.g.…”

Construction grammar for monkeys?

“…Authors et al, in preparation). Oña et al (2019), for example, suggest that multimodal gestural-facial communication in chimpanzees exhibit "componentiality" in that different combinations of gestures and facial expressions yield different communicative effects. As they argue, such componentiality is a crucial stepping stone towards compositionality.…”