Understanding audience effect in primate gestural communication (#55)
The
use of gestures by humans and other primate species is a core component of
nonverbal communication and also of high interest for both the development and
the evolution of language. Although the intentional use of gestures to
communicate might develop through experience, much less is known about its
underlying mechanisms. We drew on different experimental situations of a
food-requesting paradigm to elucidate this issue in olive baboons (Papio anubis). The first experiment
investigated whether baboons selectively gestured towards an attentive
audience. After being trained in gesturing, baboons were exposed to varied test
conditions in which the experimenter adopted different attentional states. We
showed that baboons tailored their gestures to the sheer visual attention of the
human, using the state of the eyes (open or closed) as a relevant cue to
attention. More visual gestures were observed in front of a visually attending
human, whilst acoustic gestures were rather produced when the experimenter
could not see them. Such elaboration in acoustic signalling to compensate for
communication breakdown offers solid evidence of intentional and flexible use
of gestures by these monkeys. The second experiment addressed the influence of previous experience with humans
on baboons’ gestural communication. Using another group of subjects, we
manipulated the human cues to attention the baboons were exposed to during the
training, and then examined their discriminatory skills of human attentional
states. We found that discriminatory abilities were deeply affected by the cues
to attention encountered during the training, highlighting the role of
experience in this process. In sum, monkeys trained by an attentive human match
the criteria of intentional communication set in human children, whilst monkeys
put aside from this experience do not. This provides an exciting developmental framework
to primate intentional communication and suggests that individual rearing
conditions are an essential component of it.