title: Social Use of Facial Expressions in Hylobatids.
abstract: Non-human primates use various communicative means in interactions with others. While primate gestures are commonly considered to be intentionally and flexibly used signals, facial expressions are often referred to as inflexible, automatic expressions of affective internal states. To explore whether and how non-human primates use facial expressions in specific communicative interactions, we studied five species of small apes (gibbons) by employing a newly established Facial Action Coding System for hylobatid species (GibbonFACS). We found that, despite individuals often being in close proximity to each other, in social (as opposed to non-social contexts) the duration of facial expressions was significantly longer when gibbons were facing another individual compared to non-facing situations. Social contexts included grooming, agonistic interactions and play, whereas non-social contexts included resting and self-grooming. Additionally, gibbons used facial expressions while facing another individual more often in social contexts than non-social contexts where facial expressions were produced regardless of the attentional state of the partner. Also, facial expressions were more likely 'responded to' by the partner's facial expressions when facing another individual than non-facing. Taken together, our results indicate that gibbons use their facial expressions differentially depending on the social context and are able to use them in a directed way in communicative interactions with other conspecifics.
authors.affiliation: Dept. of Education and Psychology, Freie Universität Berlin, Berlin, Germany.
authors.forename: Linda
authors.initials: L
authors.lastname: Scheider
authors.affiliation: Dept. of Psychology, University of Portsmouth, Portsmouth, United Kingdom.
authors.forename: Bridget M
authors.initials: BM
authors.lastname: Waller
authors.affiliation: Dept. of Natural Science and Mathematics, University of Groningen, Groningen, The Netherlands.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Oña
authors.affiliation: Dept. of Physical Therapy, Duquesne University, Pittsburgh, Pennsylvania, United States of America.|Dept. of Anthropology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Burrows
authors.affiliation: Dept. of Education and Psychology, Freie Universität Berlin, Berlin, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Liebal
mesh_terms: D000819:Animal Communication; D000818:Animals; D005149:Facial Expression; D005260:Female; D006922:Hylobates / Q000502:physiology / Q000523:psychology*; D008297:Male; D012919:Social Behavior; D013045:Species Specificity; D013997:Time Factors