People and horses have been known to develop close bonds: Think Gandalf and Shadowfax, or Katy McLaughlin and Flicka, or, you know, the guy who’s currently dating his horse. And it turns out that (some of) these bonds might be based on more than sugar cubes: A new study suggests that, much like dogs, horses can understand, and even respond to, human facial expressions.
It’s pretty well documented that horses respond to each other’s facial expressions, but a team of psychologists at Sussex University claims to have reported the first-ever evidence of horses responding both behaviorally and physiologically to facial expressions in people. According to a paper published in Biology Letters, when a horse is shown a photo of a negative human face its heart rate increases significantly, suggesting a marked spike in its stress levels — in other words, horses stress out when they perceive humans to be mad at them. They also tend to look at negative faces primarily with their left eye, meaning the image is processed by the right side of the brain. In horses (and in dogs), this side of the brain is generally used to process and react to antagonistic encounters, suggesting horses clearly see negative human faces as threatening.
To reach this conclusion, researchers studied 28 horses from riding and boarding stables in Sussex and Surrey between April 2014 and February 2015. (The study followed guidelines set forth by the Association for the Study of Animal Behavior and was approved by an ethics committee.) Each horse was brought in for two measurement sessions: one for one set of stimuli, and another at least two months later for the other set of stimuli. Upon arrival, each horse was led into a stable stall on a loose lead rope and had its baseline heart rate measured. It was then shown either a positive (happy) face or a negative (angry) face by experimenters, who themselves had never seen the photos. The horse’s heart rate was monitored and recorded, with the recording period starting five seconds before a horse was shown a photo and ending five seconds after. Heart-rate researchers also recorded a laterality index, or how much each horse turned to the left or right after seeing a photo.
“The reaction to angry facial expressions was particularly clear,” Amy Smith, a doctoral student at the university, told The Guardian. “There was a quicker increase in their heart rate [when they saw the angry face], and the horses moved their heads to look at the angry faces with their left eye. What’s really interesting about this research is that it shows horses have the ability to read emotions across the species barrier.” Interestingly, a horse’s response to positive facial expressions was much less clear — there was no significant lateralized response to happy faces. As the researchers suggest, this might be because positive expressions aren’t as evolutionarily significant as negative ones; if someone looks at you in a positive way, they’re unlikely to want to cause you harm, therefore there’s no immediate threat to your ability to survive and reproduce.
So why do horses care what we think? There are two possibilities: Either they’ve evolved alongside humans for so long that it’s evolutionarily beneficial for them to be able to read human faces — or perhaps each individual horse learns how to read its owner’s expressions over time. Either way, it’s becoming more clear that emotional intelligence isn’t strictly a human thing.