Can Ponies (Equus Caballus) Distinguish Human Facial Expressions?

Abstract

Simple SummaryFacial expressions communicate a great deal of information that can potentially convey the affective state of the sender and facilitate approach or avoidance responses by the receiver. Reading facial expressions across species is particularly relevant for domesticated animals who rely on humans for food, shelter, safety and social relationships. In this study, 20 ponies were individually presented with facial expressions of anger, joy, sadness and neutral by two different live actors. The ponies looked with their left eye first, more often and for longer to angry expressions and with their right eye first to joy, in keeping with the theory of lateralized responses (i.e., the right brain hemisphere is activated by stimuli on the left and is predominant in emotionalized responses). The ponies distinguished between the actors, favouring one actor with shorter looking and approach times and fewer oral behaviours. Ponies with more experience as a lesson mount had lower heart rates and lower head carriage although they exhibited more oral behaviours and kept their ear on the actor more. Ponies clearly distinguish among human facial expressions but other factors also contribute to their responses to humans.Communication within a species is essential for access to resources, alerting to dangers, group facilitation and social bonding; human facial expressions are considered to be an important factor in one’s ability to communicate with others. Evidence has shown that dogs and horses are able to distinguish positive and negative facial expressions by observing photographs of humans, however there is currently no research on how facial expressions from a live human are perceived by horses. This study investigated how ponies distinguish facial expressions presented by live actors. Trained actors (n = 2), using the human Facial Action Coding System, displayed four facial expressions (anger, sadness, joy and neutral) individually to twenty ponies. Heart rate and behaviors of the ponies including first monocular eye look, eye look duration (right and left side bias) and latency to approach were observed. A generalized linear mixed model (GLIMMIX) using Sidak’s multiple comparisons of least squared means determined that when exposed to anger expressions ponies looked more often with their left eye first and when exposed to joy, looked more often with their right eye first (p = 0.011). The ponies spent more time looking at angry expressions (p = 0.0003) in comparison to other expressions. There was no variation in heart rate across expressions (p > 0.89). Regardless of human facial expression, ponies looked longer (p = 0.0035), took longer to approach (p = 0.0297) and displayed more oral behaviours (p < 0.0001) with one actor than the other indicating increased arousal or negative valence. Ponies with more experience as a lesson mount had lower heart rates (p < 0.0001) carried their head lower (p < 0.0001), kept their left ear on the actor (p < 0.03) and exhibited more oral behaviours (p < 0.0001) than ponies with less experience. This study demonstrates that ponies are able to distinguish facial expressions presented by a live human, but other factors also contribute to their responses to humans.