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- Operationalizing intentionality in primate communication: Social and ecological considerationsPublication . Rodrigues, Evelina Daniela; Fröhlich, MarlenAn 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.
- Connecting primate gesture to the evolutionary roots of language: A systematic reviewPublication . Rodrigues, Evelina Daniela; Santos, António J.; Veppo, Flávia; Pereira, Joana; Hobaiter, CatherineComparative psychology provides important contributions to our understanding of the origins of human language. The presence of common features in human and nonhuman primate communication can be used to suggest the evolutionary trajectories of potential precursors to language. However, to do so effectively, our findings must be comparable across diverse species. This systematic review describes the current landscape of data available from studies of gestural communication in human and nonhuman primates that make an explicit connection to language evolution. We found a similar number of studies on human and nonhuman primates, but that very few studies included data from more than one species. As a result, evolutionary inferences remain restricted to comparison across studies. We identify areas of focus, bias, and apparent gaps within the field. Different domains have been studied in human and nonhuman primates, with relatively few nonhuman primate studies of ontogeny and relatively few human studies of gesture form. Diversity in focus, methods, and socio‐ecological context fill important gaps and provide nuanced understanding, but only where the source of any difference between studies is transparent. Many studies provide some definition for their use of gesture; but definitions of gesture, and in particular, criteria for intentional use, are absent in the majority of human studies. We find systematic differences between human and nonhuman primate studies in the research scope, incorporation of other modalities, research setting, and study design. We highlight eight particular areas in a call to action through which we can strengthen our ability to investigate gestural communication's contribution within the evolutionary roots of human language.
- Exploring greetings and leave-takings: communication during arrivals and departures by chimpanzees of the Bossou community, GuineaPublication . Rodrigues, Evelina Daniela; Santos, António J.; Hayashi, Misato; Matsuzawa, Tetsuro; Hobaiter, CatherineIn human fission–fusion societies, ritualized non-linguistic signal exchanges that include gestures, vocalizations, and facial expressions are regularly observed at both arrivals (greetings) and departures (leave-takings). These communicative events play an important role in the formation and maintenance of social relationships. Wild chimpanzees also form large communities that split into smaller fluid parties during daily activities, with individuals moving freely between them. However, in chimpanzees only greetings have been reported. This study explores signal exchanges in the Bossou chimpanzee community during fissions (departures) and fusions (arrivals) given an individual’s social rank, kinship, position as traveller or party-member, the level of potential threat, and the party size and presence of mature males. We analysed three time periods (1993–1994; 2003–2004; 2013–2014) during which the composition and social hierarchy of the community varied. We show that the occurrence and form of communication during fission and fusion events are mediated by social factors, including rank, kinship, and party size and composition. Individuals were more likely to communicate during fusions than during fissions, communication was more likely to be produced towards a higher-ranking individual and to non-kin individuals, but the tendency to communicate in general increased with an increase in social rank. The presence of more individuals, and in particular mature males, decreased the likelihood of communication. Communication during fusions supported patterns reported in previous studies on greetings, and our results support the argument that, if present, leave-takings are not a common feature of chimpanzee social interactions. Current methodological difficulties regarding the function of declarative signals hinder our ability to discriminate potential parting rituals within communication before departures. Given similar methodological difficulties, we also provide a note of caution in the interpretation of all signals produced during fusions as ‘greetings’.
- Communicative gestures in 7–12‐month infants: A phylogenetic comparative approachPublication . Rodrigues, Evelina Daniela; Maroco, João; Frota, SóniaDifferent methodologies applied in human and non-human primate studies limit the comparisons that can be made. The early communicative gestures of 10 children between 7 and 12 months were analysed using a descriptive approach usually found in non-human primate studies. Silent-visual gestures were the most used, followed by contact and audible gestures. The use of the different modalities of gestures did not differ with the infants' gender or age, unlike findings from studies on great apes. However, signalers chose different gestural sensory modalities according to the attentional state of the audience, similarly to other great apes: more silent-visual gestures were used when the visual attention of the recipient is present. Thus, intentionality in gestural communication was not only detected through behavioural cues but also supported by the use of different strategies according to the attentional state of the recipient. Importantly, this study suggests that human infants consider the attentional state of their partners during communication earlier in ontogeny than previously thought.