London, June 11 (IANS): Chimpanzees are able to use facial expressions and vocalisations flexibly, notably during physical contact play, says a new study.

The ability to flexibly produce facial expressions and vocalisations has a strong impact on the way humans communicate, but scientists' understanding of non-human primate facial expressions and vocalisations is limited.

The authors investigated whether chimpanzees produce the same types of facial expressions with and without accompanying vocalisations, as do humans.

Forty six chimpanzees were video-recorded during spontaneous play at the Chimfunshi Wildlife Orphanage, Zambia. ChimpFACS, a standardized coding system, was applied to measure chimpanzee facial movements, based on Facial Action Coding System (FACS) developed for humans.

Published in the open-access journal PLOS ONE, the data showed that chimpanzees produced the same 14 open mouthed facial expressions when laugh sounds were present as when they weren't.

Based on the data, the authors suggest that chimpanzees produce these facial expressions flexibly, without being constrained by the accompanying vocalisations.

Furthermore, the data indicated that the facial expression in addition to vocalisation, as well as the facial expression alone, were used differently in social play, for instance, when in physical contact with playmates and when matching playmates' open mouthed faces.

"These findings support the idea that chimpanzees produce distinctive facial expressions independently from a vocalization, and that their use affects communicative meaning, as both traits are important for a more explicit and versatile way of communicating," said lead researcher Marina Davila-Ross from the University of Portsmouth, England.