Evolution of Communication - Volume 1, Issue 2, 1997

Language develops in infancy as emerging cognitive abilities come on-line to handle the infant's experience of the world, and thereby enrich it. The attentional and motivational structuring of that experience is elaborated in the course of social interaction, but from a base in the a priori values that 'being an infant' create as to what infants find 'interesting' in their experiential worlds. There is a continuity of experience, but a reworking of it that yields apparently discontinuous stages. These stages do not map onto traditional notions such as preverbal stage, one-word stage, and combinatorial stage, but are more appropriately captured as presymbolic, symbolic, and propositional. Thus, some early word uses are pre-symbolic, and some later non-verbal gestures are propositional: that the production media might differ for words versus gestures does not appear to be a fact of major significance.

Communication by facial expressions and body postures plays an important role in the social dynamics of macaques. Macaques use gestures to mediate both competitive and cooperative interactions with other group members. Gestures convey information on the emotional state of the sender and its impending behavior but can also be used to inhibit the behavior of another individual or to request its participation in specific activities such as grooming, agonistic support, mating or play. Although most gestures are used to mediate simple approach and avoidance interactions, the size of the gestural repertoire and the subtleties of gestural communication in macaques are unparalleled in other nonprimate animals.

Observations of the gestural communication of two groups of captive chimpanzees are reported. For one group the observations represent a fourth longitudinal time point over a 12 year period; the other group was observed for the first time. There were two main questions. The first concerned how young chimpanzees use their gestures, with special foci on the flexibility displayed in signal use and on the sensitivity to audience displayed in signal choice. It was found that chimpanzees are very flexible in their signal use (different signals for same goal, same signal for different goals) and somewhat sensitive to audience (signal choice based on attentional state of recipient). The second question was how chimpanzees acquire their gestural signals. Comparisons between the two groups showed much individual variability both within and between groups. In addition, when each of the two contemporary groups was compared with the previous longitudinal time points for one of the groups, no differences in concordance were found. It was concluded that youngsters were not imitatively learning their communicatory gestures from conspecifics, but rather that they were individually ritualizing them with one another in social interaction. An experimental study in which two individuals were taught new gestures and returned to their groups — with no subsequent signs of imitation — corroborated this conclusion. Implications of the current findings for the understanding of chimpanzee communication and social learning are discussed.

The relationship between communicative gestures and language acquisition was investigated in 30 infants who were visited at home four times between 9 months and 3 years. At 9 and 15 months, they were videotaped in free play with their mothers, and their communicative gestures were coded from these interactions. At three years, measures of spontaneous speech, receptive vocabulary, and communicative competence were obtained. So-called primitive gestures, Protest/Rejection and some forms of Request, were found to decline in the second year and to be negatively related to measures of language production at 3 years. Object Exchange and Comment gestures, in contrast, increased in the second year and were positively related to language measures, the first to early vocabulary size and the second to 3-year-old receptive vocabulary. Gesturing as a whole did not decline with the onset of language, and the co-ordination of gestures with vocalizations increased. These findings support both a precursor model and an interdependent model of the relationship of gestures to language.