Vocal and visual communication and laterality: co-evolution with social systems and habitats

The wide diversity of social systems, habitat and locomotion modes of the primate species we study, allow us to develop an original comparative approach to investigate the origins of human language and its animal communication precursors. Our studies focus on the gestural and vocal origins of human language, considering some key characteristics (i.e., hemispheric specialization and laterality, syntax and semantics, intentionality, cultural transmission).

Manual laterality: from manipulation actions to communication gestures

Factors influencing hand preference in manipulations
Investigating manual laterality provides an insight into the evolution of brain hemisphere specialization. Our aim is to evaluate the importance of intrinsic (age and sex) and extrinsic (visual guidance, posture, manual coordination and spatial position of the object) factors on the expression of monkeys’ manual laterality. Our investigations are based on behavioural tests [FIG11] (including the QHP task - Quantifying Hand Preference task - adapted for primates) to assess manual laterality in various contexts.

behavioural tests

Communication gestures and intentional communication
We investigate non-human primates’ manual preferences in communication gestures between conspecifics and towards humans. We study relationships between referential pointing skills and manual preferences to point at and to grasp an object [FIG12].

relationships between referential pointing skills and manual preferences to point at and to grasp an object

Moreover, we evaluate intentionality of begging gestures of different species [FIG13], through the subjects’ consideration of an experimenter’s attentional state.

begging gestures of different species

Into the roots of human language: precursors in non-human primates’ vocal communication

Combining vocal units to compensate a limited flexibility

A crucial step in language emergence may have been the ability to combine vocal units to enhance vocal communication despite the limits of primates’ vocal flexibility. Two ways to reach this goal are explored: the use of a suffixation-like system to form more complex calls and concatenation into long vocal sequences of basic and complex calls. We aim to identify proto-semantic [FIG14], -syntactic, and -prosodic features in these sequences.

identify proto-semantic

Populational variations and cultural transmission
Dialects (socially and geographically based within-language variations) are one of the long-established parallels between human language and animal communication, mainly songbirds. We investigate primates’ possibilities to develop dialects at the semantic level when differences between populations cannot be explained by habitat or genetic variations. Geographical variations are not only sought for humans’ and non-human primates’ languages, but also for their gestural communication systems. [FIG15] On an evolutionary level, we aim to connect social complexity and vocal complexity through cross-species studies of non-human primates.

Geographical variations

Main features

  • Methodological development to test laterality in non-human primates. [FIG11]
  • Hand preference varies in relation to the position of the object and the gesture (grasping or pointing). [FIG12]
  • Mangabeys take humans’ attentional states into account and use begging gestures intentionally. [FIG13]
  • “Affixation-like” ability of free-ranging male Campbell’s monkeys. [FIG14]
  • Behavioural innovation and cultural transmission of an audio-visual signal by free-ranging black howler monkeys. [FIG15]