Multimodal communication in chimpanzees

A fundamental characteristic of human language is multimodality. In other words, humans use multiple signaling channels concurrently when communicating with one another. For example, people frequently produce manual gestures while speaking, and the words a person perceives are impacted by visual information. For this study, we hypothesized that similar to the way that humans regularly couple their spoken utterances with gestures and facial expressions, chimpanzees regularly produce vocalizations in conjunction with other communicative signals. To test this hypothesis, data were collected from 101 captive chimpanzees living in mixed-sex social groupings of seven to twelve individuals. A total of 2,869 vocal events were collected. The data indicate that approximately 50% of the vocal events were produced in conjunction with another communicative modality. In addition, approximately 68% were directed to a specific individual, and these directed vocalizations were more likely to include a signal from another communicative modality than were vocalizations that were not directed to a specific individual. These results suggest that, like humans, chimpanzees often pair their vocalizations with signals from other communicative modalities. In addition, chimpanzees appear to use their communicative signals strategically to meet specific socio-communicative ends, providing support for the growing literature that indicates that at least some chimpanzee vocal signaling is intentional.