Abstract
There is substantial evidence that both human infants and chimpanzees incorporate objects into their social interactions, with some accounts pointing to notable changes in their communication patterns related to object use. In this thesis, by adopting a comparative-developmental approach I investigate the patterns of communicative behaviours involving objects in early human and chimpanzee ontogeny. A number of factors contribute to the language development of human infants, of which protophones, a kind of speech-like vocalisations, have been found to play a considerable role that supports the emergence of linguistic skills. There seem to be some indication that protophones may be linked to certain objects, yet our understanding is limited to the expression of infant vocalisations in the context of social interactions involving various types of toys. To assess the possibility of further variation in the effect of objects on children’s early communication I examined whether the communicative expressions of infants that live in the traditional societies of rural Zambia differ when interacting with natural objects, household items, and toys. Here, for the first time, I expand this scope to natural and artificial objects, providing evidence that the infants’ production of precursors to speech, protophones, may be encouraged by interactions involving artificial objects. This supports the view that the physical environment, and not just the social environment, can promote on its own the production of protophones in young children, thus also possibly contributing to their language development. Yet, the current work indicates further complexity linked to the protophone activity in object communication, where protophones may serve as attention-getting behaviours for certain types of object signals. The findings of my second study showed that the infants’ protophones are used predominantly when object signalling occurs as part of a silent-visual modality, a pathway, that seems to also trigger the responses in the caretakers most efficiently. It is therefore possible that the attention-getting properties of protophones may also extend to object communication in response to silent-visual signalling. Ultimately, the findings on protophones, the known precursors to language, offer new insights on how objects may help promote language development, particularly in relation to the usage of artificial objects, in the form of attention-getting behaviours. Finally, I also found evidence that that chimpanzees may communicate differently on account of specific sets of objects.The findings of my comparative study showed that artificial, less familiar objects may promote communicative expressions more than natural objects in young chimpanzees, who seem to favour the former, perhaps due to its appealing features. Together, this suggests that certain sets of objects have the potential to induce communicative behaviours more than others. These findings offer valuable clues into how the use of objects in social interactions may help to promote the development of facial and vocal expressions in chimpanzees, in a comparable way to which they promote the development of language in human infants.
| Date of Award | 25 May 2023 |
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| Original language | English |
| Supervisor | Marina Davila Ross (Supervisor), Eszter Somogyi (Supervisor) & Iris Nomikou (Supervisor) |