Intentional gestural communication amongst red-capped mangabeys (Cercocebus torquatus)

Abstract

Apes, human’s closest living relatives, are renowned for their intentional and highly flexible use of gestural communication. In stark contrast, evidence for flexible and intentional gestural communication in monkeys is scarce. Here, we investigated the intentionality and flexibility of spontaneous gesture use in red-capped mangabeys (Cercocebus torquatus). We applied established methods used in ape gesture research to analyse whether the body acts produced by a total of 17 individuals living in three different groups in captivity qualified as intentionally produced gesture instances. Results showed that signallers showed all hallmarks of intentionality during the production of 20 out of a total of 21 different types of body acts. These were only produced in the presence of other individuals, and the monkeys showed audience checking, sensitivity to the attentional states of recipients, adjustment of signal modality, and response waiting relative to their production. Moreover, in case of communication failure, the monkeys showed goal persistence, and regarding the production contexts they showed some signs of means–ends dissociation. Therefore, these monkeys are capable of flexible and intentional gestural communication and use this to communicate with conspecifics. Our results corroborate recent findings showing that intentional gestural communication was already present in the monkey lineage of catarrhine primates. We discuss our results in light of the comparative approach towards human language evolution and highlight our finding that these monkeys also showed flexible and intentional use of four ‘free’ manual gesture types.

Facial displays in red-capped mangabeys (Cercocebus torquatus): Repertoire, social context, and potential intentionality.

“…Bard (1992) introduced Bates' definition of intentional communication to the study of primate communication, distinguishing intentional communication from other intentional behaviors in orangutan mother-infant interactions. In the same line, several behavioral indices of intentional communication inherited from child developmental studies were then applied to nonhuman gestural studies to assess intentionality (see, for reviews, Byrne et al, 2017;Leavens, Russell, & Hopkins, 2005;Liebal, Waller, Burrows, & Slocombe, 2014c;Schel, Bono, Aychet, Pika, & Lemasson, 2020;Townsend et al, 2017). Townsend et al (2017) recently gathered these indices in a general framework implying three main criteria to attribute intentionality to communicative signals: The signal has to be directed toward a recipient, produced to reach a particular social goal, and has to be followed by a response from the recipient that is consistent with the goal that is deduced for the signaler.…”

“…A signal is considered as recipient-directed if it is produced in the presence of potential receivers (i.e., "socially used") and physically directed to another individual (Call & Tomasello, 2007;Leavens & Hopkins, 1998;Leavens, Hopkins, & Bard, 1996;Leavens, Hopkins, & Thomas, 2004;Liebal et al, 2014a;Schel et al, 2020;Tomasello et al, 1985;Tomasello, Call, Nagell, Olguin, and Carpenter, 1994). To discriminate socially dependent signals from others, supplementary indicators should be taken into account, such as the fact that the signaler first checked the audience's attentional state before producing the display (Genty et al, 2009;Graham et al, 2017;Hobaiter & Byrne, 2011a;Schel et al, 2020), at least in case of signals that have to be perceived on the visual channel.…”

“…A signal is considered as recipient-directed if it is produced in the presence of potential receivers (i.e., "socially used") and physically directed to another individual (Call & Tomasello, 2007;Leavens & Hopkins, 1998;Leavens, Hopkins, & Bard, 1996;Leavens, Hopkins, & Thomas, 2004;Liebal et al, 2014a;Schel et al, 2020;Tomasello et al, 1985;Tomasello, Call, Nagell, Olguin, and Carpenter, 1994). To discriminate socially dependent signals from others, supplementary indicators should be taken into account, such as the fact that the signaler first checked the audience's attentional state before producing the display (Genty et al, 2009;Graham et al, 2017;Hobaiter & Byrne, 2011a;Schel et al, 2020), at least in case of signals that have to be perceived on the visual channel. Furthermore, the sensitivity to the attentional state of the recipient, both regarding the rate or the modality of the signal, is often studied as an indicator of intentional use of gestures (Bourjade, Meguerditchian, Maille, Gaunet, & Vauclair, 2014;Demuru, Ferrari, & Palagi, 2015;Leavens, Hostetter, Wesley, & Hopkins, 2004;Maille, Engelhart, Bourjade, & Blois-Heulin, 2012;Meunier, Prieur, & Vauclair, 2013;Poss et al, 2006).…”

“…Furthermore, the sensitivity to the attentional state of the recipient, both regarding the rate or the modality of the signal, is often studied as an indicator of intentional use of gestures (Bourjade, Meguerditchian, Maille, Gaunet, & Vauclair, 2014;Demuru, Ferrari, & Palagi, 2015;Leavens, Hostetter, Wesley, & Hopkins, 2004;Maille, Engelhart, Bourjade, & Blois-Heulin, 2012;Meunier, Prieur, & Vauclair, 2013;Poss et al, 2006). The second dimension of intentional communication, that is, the goal-directedness of the signal, could be checked by monitoring response-waiting from the signaler after it produced the display (Call & Tomasello, 2007;Cartmill & Byrne, 2010;Graham et al, 2017;Hobaiter & Byrne, 2011a;Molesti, Meguerditchian, & Bourjade, 2020;Pika, Liebal, & Tomasello, 2003;Roberts et al, 2014;Roberts, Vick, Roberts, Buchanan-Smith, & Zuberbühler, 2012;Schel et al, 2020;Tomasello et al, 1985Tomasello et al, , 1994. Moreover, goal-directedness is recognized when the signaler stops producing the signal once the presumed goal has been reached, and repeats and/or elaborates the signals in case the goal has not been met yet (Cartmill & Byrne, 2007Genty, Clay, Hobaiter, & Zuberbühler, 2014;Graham et al, 2017;Gupta & Sinha, 2019;Hobaiter & Byrne, 2011b;Hostetter et al, This document is copyrighted by the American Psychological Association or one of its allied publishers.…”

“…Based on these indices, the intentionality of great apes' communication gestures has been admitted, notably from 's work on chimpanzee sensitivity to the receiver's attentional state when gesturing, followed by numerous field and lab studies on great apes (see, for reviews, Byrne et al, 2017;Call & Tomasello, 2007;Liebal et al, 2014c). Intentional gestures have been explored recently in monkey species such as macaques (Macaca mulatta, tonkeana, andradiata, Canteloup, Bovet, &Meunier, 2015a, 2015b;Deshpande, Gupta, & Sinha, 2018;Gupta & Sinha, 2019), olive baboons (Papio anubis, Bourjade et al, 2014;Meunier et al, 2013;Molesti et al, 2020), red-capped mangabeys (Cercocebus torquatus, Aychet et al, 2020;Maille et al, 2012;Schel et al, 2020), squirrel monkeys (Saimiri sciureus, Anderson, Kuroshima, Hattori, & Fujita, 2010). However, studies of potential intentionality markers accompanying the production of primates' facial expressions are still rare.…”