Inferential Communication: Bridging the Gap Between Intentional and Ostensive Communication in Non-human Primates

Communication, when defined as an act intended to affect the psychological state of another individual, demands the use of inference. Either the signaler, the recipient, or both must make leaps of understanding which surpass the semantic information available and draw from pragmatic clues to fully imbue and interpret meaning. While research into human communication and the evolution of language has long been comfortable with mentalistic interpretations of communicative exchanges, including rich attributions of mental state, research into animal communication has balked at theoretical models which describe mentalized cognitive mechanisms. We submit a new theoretical perspective on animal communication: the model of inferential communication. For use when existing proximate models of animal communication are not sufficient to fully explain the complex, flexible, and intentional communication documented in certain species, specifically non-human primates, we present our model as a bridge between shallower, less cognitive descriptions of communicative behavior and the perhaps otherwise inaccessible mentalistic interpretations of communication found in theoretical considerations of human language. Inferential communication is a framework that builds on existing evidence of referentiality, intentionality, and social inference in primates. It allows that they might be capable of applying social inferences to a communicative setting, which could explain some of the cognitive processes that enable the complexity and flexibility of primate communication systems. While historical models of animal communication focus on the means-ends process of behavior and apparent cognitive outcomes, inferential communication invites consideration of the mentalistic processes that must underlie those outcomes. We propose a mentalized approach to questions, investigations, and interpretations of non-human primate communication. We include an overview of both ultimate and proximate models of animal communication, which contextualize the role and utility of our inferential communication model, and provide a detailed breakdown of the possible levels of cognitive complexity which could be investigated using this framework. Finally, we present some possible applications of inferential communication in the field of non-human primate communication and highlight the role it could play in advancing progress toward an increasingly precise understanding of the cognitive capabilities of our closest living relatives.

Operationalizing Intentionality in Primate Communication: Social and Ecological Considerations

An intentional transfer of information is central to human communication. When comparing nonhuman primate communication systems to language, a critical challenge is to determine whether a signal is used in intentional, goal-oriented ways. As it is not possible to directly observe psychological states in any species, comparative researchers have inferred intentionality via behavioral markers derived from studies on prelinguistic human children. Recent efforts to increase consistency in nonhuman primate communication studies undervalue the effect of possible sources of bias: some behavioral markers are not generalizable across certain signal types (gestures, vocalizations, and facial expressions), contexts, settings, and species. Despite laudable attempts to operationalize first-order intentionality across signal types, a true “multimodal” approach requires integration across their sensory components (visual-silent, contact, audible), as a signal from a certain type can comprise more than one sensory component. Here we discuss how the study of intentional communication in nonlinguistic systems is hampered by issues of reliability, validity, consistency, and generalizability. We then highlight future research avenues that may help to understand the use of goal-oriented communication by opting, whenever possible, for reliable, valid, and consistent behavioral markers, but also taking into account sampling biases and integrating detailed observations of intraspecific communicative interactions.

The Vocal Repertoire of the Bearded Capuchin (Cebidae: Sapajus libidinosus): Implications for Understanding the Complexity of Neotropical Primate Communication

Vocal communication is an essential aspect of primate social behaviour. The bearded capuchin <i>Sapajus libidinosus</i> is endemic to Brazil, and some studies have described specific vocalisation types for this species; however, there is still no complete description of its vocal repertoire. Thus, this study aimed to describe the vocal repertoire of a group of <i>S. libidinosus</i> living in the<i></i>Parque Nacional de Brasília, a protected area in the Cerrado area of Central Brazil. We carried out focal samplings and recording of vocalisations of members of an <i>S. libidinosus</i> troop in different behavioural contexts. The call analyses revealed 25 different types of vocalisations, and each call presented significant structural variation. We grouped these vocalisations according to the context of the emission or acoustic structure into the following categories: contact calls (contact note, infant babbling, trill, teeth- and lip-smacking, and sirena); foraging calls (chihui, grgr, and patinado); whistle series (food-associated, long-distance, and intergroup encounter); aggressive calls (aggressive contact note, ascending rapid staccato, cough cough, and pip); calls in response to aggression (scream, squeal, and pulsed scream), sexual display calls (chuck and raspy oestrous call), and stress-related calls (alarm call/bark, hiccup, hip, double hip, and wah wah). <i>S. libidinosus</i> presented a very rich vocal repertoire, revealing a pattern consistent with the repertoire of other capuchin monkey species. This is the first comprehensive description of the<i> S. libidinosus</i> vocal repertoire and highlights the complexity of neotropical primate communication.

Operationalizing intentionality in primate communication: Social and ecological considerations

An intentional transfer of information is central to human communication. When comparing nonhuman primate communication systems to language, a critical challenge is to determine whether a signaller intends for the recipient to derive a particular meaning from the message contained in the signal. As it is not possible to directly observe psychological states in any species, comparative researchers have inferred intentionality via behavioural markers derived from studies on pre-linguistic human children. Recent efforts to increase consistency between nonhuman primate communication studies undervalue the effect of possible sources of bias: some behavioural markers are not generalizable across certain signal types (gestures, vocalizations, and facial expressions), contexts, settings and species. Despite laudable attempts to operationalise first-order intentionality across signal types, a true “multimodal” approach requires integration across their sensory components (visual-silent; contact; audible), as a signal from a certain type can comprise more than one sensory component. Here we discuss how the study of intentional communication in non-linguistic systems is hampered by issues of reliability, validity, consistency, and generalizability. We then highlight future research avenues that may help to understand the use of goal-oriented communication by opting, whenever possible, for reliable, valid, and consistent behavioural markers, but taking into account sampling biases and integrating detailed observations of intra-specific communicative interactions.

Primate Vocal Communication and the Evolution of Speech

Studies of nonhuman primate communication are often motivated by the desire to shed light on the evolution of speech. In contrast to human speech, the vocal repertoires of nonhuman primates are evolutionarily highly conserved. Within species-specific constraints, calls may vary in relation to the internal state of the caller or social experience. Receivers can use signalers’ calls to predict upcoming events or behavioral dispositions. Yet nonhuman primates do not appear to express or comprehend communicative or informative intent. Signalers are sensitive to the relation between their own actions and receivers’ responses, and thus, signaling behavior can be conceived as goal directed. Receivers’ ability to integrate information from multiple sources renders the system flexible and powerful. Researchers who take a linguistic or biological perspective on nonhuman primate communication should be aware of the strengths and limitations of their approaches. Both benefit from a focus on the mechanisms that underpin signaling and responses to signals.

What is a gesture? A lesson from comparative gesture research

Research into nonhuman primates’ gestures is often limited by the lack of clear criteria to define a gesture and by studying gestures separately from other communicative means. Despite the fundamental differences between the gestural communication of humans and other primates, I argue that sign language research might benefit from the lessons learned from these drawbacks and the current developments in primate communication research.