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Scientific reports2023; 13(1); 8625; doi: 10.1038/s41598-023-35807-z

Horses (Equus caballus) facial micro-expressions: insight into discreet social information.

Abstract: Facial micro-expressions are facial expressions expressed briefly (less than 500 ms) and involuntarily. Described only in humans, we investigated whether micro-expressions could also be expressed by non-human animal species. Using the Equine Facial action coding system (EquiFACS), an objective tool based on facial muscles actions, we demonstrated that a non-human species, Equus caballus, is expressing facial micro-expressions in a social context. The AU17, AD38 and AD1 were selectively modulated as micro-expression-but not as standard facial expression (all durations included)-in presence of a human experimenter. As standard facial expressions, they have been associated with pain or stress but our results didn't support this association for micro-expressions which may convey other information. Like in humans, neural mechanisms underlying the exhibit of micro-expressions may differ from those of standard facial expressions. We found that some micro-expressions could be related to attention and involved in the multisensory processing of the 'fixed attention' observed in horses' high attentional state. The micro-expressions could be used by horses as social information in an interspecies relationship. We hypothesize that facial micro-expressions could be a window on transient internal states of the animal and may provide subtle and discreet social signals.
© 2023. The Author(s).
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Publication Date: 2023-05-27 PubMed ID: 37244937PubMed Central: PMC10224940DOI: 10.1038/s41598-023-35807-zGoogle Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research paper investigates the existence and implications of facial micro-expressions in horses (Equus caballus). Previously documented only in humans, the study demonstrates that horses too express these brief and involuntary facial cues, especially in social contexts involving human presence.

Research Methodology

  • The study utilized the Equine Facial action coding system (EquiFACS), an analytical tool that assesses facial expressions based on muscle movements.
  • The micro-expressions of the horses were observed and evaluated in a social setting involving a human experimenter.
  • Specific muscle movements known as AU17, AD38, and AD1 were heavily monitored. These movements were identified as possible micro-expressions but not standard facial expressions.

Findings

  • It was found that horses were indeed capable of expressing facial micro-expressions, as evidenced by the selective modulation of AU17, AD38, and AD1 in the presence of a human experimenter.
  • While these muscle movements in their standard form were typically associated with pain or stress, the study discovered that their micro-expression forms didn’t support this association, suggesting they may convey different information.
  • Some micro-expressions were linked to attention, effective in the multisensory processing of a phenomenon called ‘fixed attention’, which was observed in horses in an attentive state.
  • The research suggested that these micro-expressions could potentially be used by horses as social cues in their interactions with other species.

Implications and Hypotheses

  • Micro-expressions could provide insight into transient internal emotional states of horses.
  • They may serve as unobtrusive social signals, enhancing the communication between different species.
  • The neural mechanisms underlying micro-expressions and standard facial expressions likely differ from each other.

The findings of this study could potentially pave the way for better understanding and communication between horses and other species, particularly humans. It could also help improve our comprehension of the overall emotional states and social behaviors of horses.

Cite This Article

APA
Tomberg C, Petagna M, de Selliers de Moranville LA. (2023). Horses (Equus caballus) facial micro-expressions: insight into discreet social information. Sci Rep, 13(1), 8625. https://doi.org/10.1038/s41598-023-35807-z

Publication

Scientific reports
ISSN: 2045-2322
NlmUniqueID: 101563288
Country: England
Language: English
Volume: 13
Issue: 1
Pages: 8625
PII: 8625

Researcher Affiliations

Tomberg, Claude
  • Faculty of Medicine, Université Libre de Bruxelles, 808, Route de Lennik, CP 630, 1070, Brussels, Belgium. ctomberg@ulb.ac.be.
Petagna, Maxime
  • Faculty of Medicine, Université Libre de Bruxelles, 808, Route de Lennik, CP 630, 1070, Brussels, Belgium.
de Selliers de Moranville, Lucy-Anne
  • Faculty of Medicine, Université Libre de Bruxelles, 808, Route de Lennik, CP 630, 1070, Brussels, Belgium.

MeSH Terms

  • Humans
  • Horses
  • Animals
  • Facial Expression
  • Face
  • Facial Muscles
  • Social Environment
  • Pain

Conflict of Interest Statement

The authors declare no competing interests.

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Citations

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