Sensitivity to the communicative partner's attentional state: A developmental study on mother-infant dyads in wild chimpanzees (Pan troglodytes schweinfurthii)

Age differences in bonobo (Pan paniscus) multimodal communication signals

While spoken language is unique to humans, many features of human communication are shared with great apes, including the use of signals in multiple modalities such as vocalizations, gestures, and facial expressions. Communication signals can be unimodal (involving a single modality) or multimodal (combining multiple modalities simultaneously). Here, we examined age-related differences in bonobo (Pan paniscus) unimodal and multimodal communication signals. We assessed all vocalizations, gestures, facial expressions, and multimodal combinations produced by captive bonobos across a variety of behavioral contexts. All occurrences of communication signals were collected via focal observations from 12 individuals ranging from 6 months to 44 years of age. All individuals produced multimodal communication signals but all bonobos, regardless of age, produced multimodal signals at lower frequencies than unimodal signals. Age had a significant effect with younger bonobos producing more multimodal signals than older individuals (p < 0.001). The infant and juveniles produced the most multimodal signals and there was an approximately 6% increase in unimodal signals per age year increase. These findings indicate a developmental shift toward unimodal signals as bonobos age. Behavioral context was predictive of signal type usage with an increase of multimodal signals in agonistic (p < 0.001), play (p < 0.001), and sexual contexts (p = 0.001). This indicates that context is important for bonobo modality with multimodal signaling occurring more in "high-risk/high-reward" contexts where proper signal comprehension is vital. This study represents an overview of multimodal communication across bonobo life stages, offering further insights into primate communication patterns and developmental trajectories.

Attention-sensitive communication in 13-month-old infants from urban and rural areas in Mozambique: Influence of the recipient's behaviour and lifestyle

A handful of recent comparative studies indicates that infants' early pragmatic skills such as attention-sensitive communication (ASC), i.e., the ability to adjust the sensory modality of communicative signals to the recipient's attention, are affected by the recipient's behaviour and attentional state. However, no study has been conducted in non-western eco-cultural environments comprising several main caregivers. This study aimed to bridge this gap by examining ASC in 13-month-old Mozambican infants filmed in their homes in rural and urban communities in Mozambique. ASC was assessed through infants' ability to avoid producing a silent-visual signal towards a visually inattentive recipient (unimodal adjustment) and/or instead employ tactile-or-audible signals in such situations (cross-modal adjustment). An ethological quantitative coding of behaviour was used to test if (1) 13-month-old infants displayed ASC, (2) eco-cultural environments affected ASC abilities, (3) infants addressed their mother or a non-maternal recipient differently, and (4) ASC was of predictive value regarding subsequent language skills. Infants from both rural and urban communities displayed ASC through unimodal and cross-modal adjustments, towards their mother and non-maternal recipients. Infants' unimodal adjustment was facilitated by the mother's Infant-Directed Speech (IDS) and physical contact and by non-maternal recipients' physical contact. Cross-modal adjustment was eased by the removal of the mother's physical contact and by the removal of non-maternal recipients' IDS. Cross-modal adjustment abilities predicted a higher vocabulary production score in the MBCDI. These findings indicate that ASC is present in non-western infant development and is scaffolded on recipients' behaviours, which vary according to the recipient's status and eco-cultural environment.

Attention-sensitive signalling by 7- to 20-month-old infants in a comparative perspective

Attention-sensitive signalling is the pragmatic skill of signallers who adjust the modality of their communicative signals to their recipient's attention state. This study provides the first comprehensive evidence for its onset and development in 7-to 20-month-olds human infants, and underlines its significance for language acquisition and evolutionary history. Mother-infant dyads (N = 30) were studied in naturalistic settings, sampled according to three developmental periods (in months); [7-10], [11-14], and [15-20]. Infant's signals were classified by dominant perceptible sensory modality and proportions compared according to their mother's visual attention, infant-directed speech and tactile contact. Maternal visual attention and infant-directed speech were influential on the onset and steepness of infants' communicative adjustments. The ability to inhibit silent-visual signals towards visually inattentive mothers (unimodal adjustment) predated the ability to deploy audible-or-contact signals in this case (cross-modal adjustment). Maternal scaffolding of infant's early pragmatic skills through her infant-directed speech operates on the facilitation of infant's unimodal adjustment, the preference for oral over gestural signals, and the audio-visual combinations of signals. Additionally, breakdowns in maternal visual attention are associated with increased use of the audible-oral modality/channel. The evolutionary role of the sharing of attentional resources between parents and infants into the emergence of modern language is discussed.

Patterns of attention-sensitive communication contribute to 7-20-month-olds' emerging pragmatic skills

The present study aimed at investigating the ability of 7- to 20-month-old infants to display attention-sensitive communication using either canonical markers of language acquisition (e.g., pointing gestures, canonical babblings) or other signals based on the physical features actually perceived by the mother in everyday interaction (e.g., body movements, mouth sounds). We studied 30 French mother-infant dyads in naturalistic settings. We assessed the infants' attention-sensitive communication through unimodal and cross-modal adjustment, defined as the capacity of infants to address visually inattentive mothers by avoiding visual communication mismatches and/or favoring communication matches through audible-or-contact signals. Unimodal and cross-modal adjustments were tested for specific signals across spontaneous "conditions" of maternal visual attention (attentive/inattentive) from video footage filmed in the home. Both canonical markers of language development and signals belonging to an extended repertoire of communication were used by infants to adjust to their mother's visual attention. Gaze-coordinated signals were overall not significantly better adjusted to maternal attention than non-gaze-coordinated signals, except for specific silent-visual signals at certain ages. Overall, these results indicate that attention-sensitive communication is relevant to the development of early pragmatic skills and that the intentional use of signals may be more reliably approximated by this capacity than by gaze-coordination with signals.

GesturalOrigins: A bottom-up framework for establishing systematic gesture data across ape species

Current methodologies present significant hurdles to understanding patterns in the gestural communication of individuals, populations, and species. To address this issue, we present a bottom-up data collection framework for the study of gesture: GesturalOrigins. By "bottom-up", we mean that we minimise a priori structural choices, allowing researchers to define larger concepts (such as 'gesture types', 'response latencies', or 'gesture sequences') flexibly once coding is complete. Data can easily be re-organised to provide replication of, and comparison with, a wide range of datasets in published and planned analyses. We present packages, templates, and instructions for the complete data collection and coding process. We illustrate the flexibility that our methodological tool offers with worked examples of (great ape) gestural communication, demonstrating differences in the duration of action phases across distinct gesture action types and showing how species variation in the latency to respond to gestural requests may be revealed or masked by methodological choices. While GesturalOrigins is built from an ape-centred perspective, the basic framework can be adapted across a range of species and potentially to other communication systems. By making our gesture coding methods transparent and open access, we hope to enable a more direct comparison of findings across research groups, improve collaborations, and advance the field to tackle some of the long-standing questions in comparative gesture research.

Object use in communication of semi-wild chimpanzees

Object interactions play an important role in human communication but the extent to which nonhuman primates incorporate objects in their social interactions remains unknown. To better understand the evolution of object use, this study explored how objects are used in social interactions in semi-wild chimpanzees (Pan troglodytes). We used an observational approach focusing on naturally occurring object actions where we examined their use and tested whether the production of object actions was influenced by the recipients' visual attention as well as by colony membership. The results show that chimpanzees adjusted both the type of object used, and the modality of object actions to match the visual attention of the recipient, as well as colony differences in the use of targeted object actions. These results provide empirical evidence highlighting that chimpanzees use objects in diverse ways to communicate with conspecifics and that their use may be shaped by social factors, contributing to our understanding of the evolution of human nonverbal communication, language, and tool use.

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

How human language evolved remains one of the most intriguing questions in science, and different approaches have been used to tackle this question. A recent hypothesis, the Interaction Engine Hypothesis, postulates that language was made possible through the special capacity for social interaction involving different social cognitive skills (e.g., joint attention, common ground) and specific characteristics such as face-to-face interaction, mutual gaze and turn-taking, the exchange of rapid communicative turns. Recently, it has been argued that this turn-taking infrastructure may be a foundational and ancient mechanism of the layered system of language because communicative turn-taking has been found in human infants and across several non-human primate species. Moreover, there is some evidence for turn-taking in different mammalian taxa, especially those capable of vocal learning. Surprisingly, however, the existing studies have mainly focused on turn-taking production of adult individuals, while little is known about its emergence and development in young individuals. Hence, the aim of the current paper was 2-fold: First, we carried out a systematic review of turn-taking development and acquisition in mammals to evaluate possible research bias and existing gaps. Second, we highlight research avenues to spur more research into this domain and investigate if distinct turn-taking elements can be found in other non-human animal species. Since mammals exhibit an extended development period, including learning and strong parental care, they represent an excellent model group in which to investigate the acquisition and development of turn-taking abilities. We performed a systematic review including a wide range of terms and found 21 studies presenting findings on turn-taking abilities in infants and juveniles. Most of these studies were from the last decade, showing an increased interest in this field over the years. Overall, we found a considerable variation in the terminologies and methodological approaches used. In addition, studies investigating turn-taking abilities across different development periods and in relation to different social partners were very rare, thereby hampering direct, systematic comparisons within and across species. Nonetheless, the results of some studies suggested that specific turn-taking elements are innate, while others are acquired during development (e.g., flexibility). Finally, we pinpoint fruitful research avenues and hypotheses to move the field of turn-taking development forward and improve our understanding of the impact of turn-taking on language evolution.

Visual bodily signals as core devices for coordinating minds in interaction

The view put forward here is that visual bodily signals play a core role in human communication and the coordination of minds. Critically, this role goes far beyond referential and propositional meaning. The human communication system that we consider to be the explanandum in the evolution of language thus is not spoken language. It is, instead, a deeply multimodal, multilayered, multifunctional system that developed-and survived-owing to the extraordinary flexibility and adaptability that it endows us with. Beyond their undisputed iconic power, visual bodily signals (manual and head gestures, facial expressions, gaze, torso movements) fundamentally contribute to key pragmatic processes in modern human communication. This contribution becomes particularly evident with a focus that includes non-iconic manual signals, non-manual signals and signal combinations. Such a focus also needs to consider meaning encoded not just via iconic mappings, since kinematic modulations and interaction-bound meaning are additional properties equipping the body with striking pragmatic capacities. Some of these capacities, or its precursors, may have already been present in the last common ancestor we share with the great apes and may qualify as early versions of the components constituting the hypothesized interaction engine. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.