By Amy Smith
Undeniably, horses have funny faces. Long nose, eyes on the sides of the head, wiggly ears…morphologically they look very different to humans, yet it turns out they are pretty good at looking across the species barrier to read our faces.
The ability to read emotion in others is hugely important in daily social life, not just for humans and other primates, but for many social species. Emotions are tools of communication – for instance, if a sheep sees another sheep looking scared (bulging eyes, ears pinned back), the observer knows there is a threat nearby, and can take appropriate action (i.e. increasing vigilance and readying themselves for a ‘fight or flight’ response). On top of this, recognising emotion can help social groups stick together. Facial expressions can communicate dominance and submissiveness, so that each individual can keep their place in the dominance hierarchy.
Reading facial expressions of emotion between different species may present more challenges due to differences in facial and body structure, and in the forms which emotional signals take. For instance, sheep, horses and dogs can express and perceive emotion in one another’s ear movements (e.g. pinning their ears flat against their heads is a signal of negative emotion), whereas this mode of communication is absent in humans. Despite such differences, dogs have previously been shown to recognise human emotion from facial expressions alone – they prefer happy human faces and dislike angry ones. Here in the Mammal Vocal Communication and Cognition Research group, we set out to test if horses, too, can recognise human facial expressions of emotion.
We visited stables around Sussex and showed 28 horses photographs of positive (happy) and negative (angry) human facial expressions, whilst recording their heart rates using a Polar Equine heart rate monitor. We tested each horse twice, once with each emotion, in trials separated by at least 2 months to prevent horses getting used to the experimental setup. Two major things came through in the results: firstly, when observing the angry face, horses preferred to look with their left eye (which many species do when they are perceiving a threat in the environment); and secondly, their heart rates increased faster towards the angry face, indicating a greater degree of stress.
Overall, the horses had stronger reactions when faced with the negative than the positive expression. This same pattern is seen in dogs, who also display a left-gaze bias towards angry human faces, and also respond less to happy faces. Animals may benefit more from recognising and reacting to potential threats in the environment over positive events, particularly in a prey animal such as the horse whose ancestral survival depended on the detection of predators.
Horses’ abilities to read emotion on human faces may have resulted in part from their 6,000-year coevolution with humans. It is also possible that, during an individual’s lifetime, horses form associations between angry humans and negative treatment, such as rough handling, and therefore learn to be wary of angry humans. You could compare this to our human ability to recognise a dog’s social signals – if you see a dog snarling at you with exposed teeth, you would tend to steer clear of this individual. To get at the potential effects of learnt vs. innate explanations, one would need to test the recognition abilities of individuals with differing levels of human exposure, e.g. feral horses or very young horses.
The continuing work of the Mammal Vocal Communication and Cognition lab at Sussex (funded by the Leverhulme Trust) is looking into horses’ social and emotional lives, between horses and horses, as well as horses and humans.
Reference: “Functionally relevant responses to human facial expressions of emotion in the domestic horse (Equus caballus)” AV Smith, L Proops, K Grounds, J Wathan, K McComb 2016, Biology Letters, doi: http://dx.doi.org/10.1098/rsbl.2015.0907