GorillaFACS: the facial action coding system for the Gorilla spp.

Correia-Caeiro, C, Costa, R, Hayashi, M, Burrows, A, Pater, J, Miyabe-Nishiwaki, T, Richardson, JL, Robbins, MM, Waller, B ORCID: https://orcid.org/0000-0001-6303-7458 and Liebal, K, 2025. GorillaFACS: the facial action coding system for the Gorilla spp. PLOS ONE, 20 (1): e0308790. ISSN 1932-6203

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Abstract

The Facial Action Coding System (FACS) is an objective observation tool for measuring human facial behaviour. It avoids subjective attributions of meaning by objectively measuring independent movements linked to facial muscles, called Action Units (AUs). FACS has been adapted to 11 other taxa, including most apes, macaques and domestic animals, but not yet gorillas. To carry out cross species studies of facial expressions within and beyond apes, gorillas need to be included in such studies. Hence, we developed the GorillaFACS for the Gorilla spp. We followed similar methodology as previous FACS: First, we examined the facial muscular plan of the gorilla. Second, we analysed gorilla videos in a wide variety of contexts to identify their spontaneous facial movements. Third, we classified the individual facial movements according to appearance changes produced by the corresponding underlying musculature. A diverse repertoire of 42 facial movements was identified in the gorilla, including 28 AUs and 14 Action Descriptors, with several new movements not identified in the HumanFACS. Although some of the movements in gorillas differ from humans, the total number of AUs is comparable to the HumanFACS (32 AUs). Importantly, the gorilla’s range of facial movements was larger than expected, suggesting a more relevant role in social interactions than what was previously assumed. GorillaFACS is a scientific tool to measure facial movements, and thus, will allow us to better understand the gorilla’s expressions and communication. Furthermore, GorillaFACS has the potential be used as an important tool to evaluate this species welfare, particularly in settings of close proximity to humans.

Item Type:	Journal article
Publication Title:	PLOS ONE
Creators:	Correia-Caeiro, C., Costa, R., Hayashi, M., Burrows, A., Pater, J., Miyabe-Nishiwaki, T., Richardson, J.L., Robbins, M.M., Waller, B. and Liebal, K.
Publisher:	Public Library of Science
Date:	28 January 2025
Volume:	20
Number:	1
ISSN:	1932-6203
Identifiers:	Number Type 10.1371/journal.pone.0308790 DOI 2362090 Other
Rights:	© 2025 Correia-Caeiro et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Divisions:	Schools > School of Social Sciences
Record created by:	Jonathan Gallacher
Date Added:	29 Jan 2025 12:04
Last Modified:	29 Jan 2025 12:04
URI:	https://irep.ntu.ac.uk/id/eprint/52941

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