A new study from the University of Sussex suggests that horses have a functional understanding of basic human emotions.
Researchers from the University's Mammal Vocal Communication and Cognition Research Group showed 28 horses photographs of happy and angry human faces. They studied the horses' physical and physiological reactions to the photos.
Based on the horses' responses to the photos, the researchers found that the horses were able to distinguish between happy and angry human facial expressions. The horses were particularly responsive to the negative photos.
Researchers noted that the horses experienced an elevated heart rate and other stress-induced behaviors in response to the negative facial expressions. This study is the first instance of a relationship between animal heart rate and human facial expressions in studies of human/animal interaction.
In addition to exhibiting physiological signs of stress when shown the angry faces, the horses viewed those photos primarily with their left eye, which is a behavior that has also been observed in dogs. The right hemisphere of the brain processes information received by the left eye.
Moreover, it is also the brain's right hemisphere that processes potentially threatening stimuli. Using the left eye to view negative or threatening information is a phenomenon that has been documented in multiple species.
Doctoral student Amy Smith, a co-leader of the research, believes the horses' strong reaction to the negative photos is, in part, a function of evolution. Being able to identify potential dangers or threats in its environment can mean the difference between life and death for an animal.
"In this context, recognizing angry faces may act as a warning system, allowing horses to anticipate negative human behavior such as rough handling," Smith said.
Professor Karen McComb, co-lead author of the research, offered several possible explanations for the study's findings. Being a socially sophisticated species, horses have long been able to read and respond to each other's emotional cues. It's possible, she said, that as horses co-evolved with humans, horses might have adapted that ability to read and respond to such cues in humans.
An alternative explanation is that the ability to read human emotions might be a more individualized skill, learned over the course of an individual horse's lifetime. Regardless of its origin, the ability is remarkable.
"What's interesting is that accurate assessment of a negative emotion is possible across the species barrier despite the dramatic difference in facial morphology between horses and humans," McComb noted.
The team's research into the emotional capacities of highly social species is ongoing. Next steps will examine the linkages between animals' emotional awareness and a variety of social behaviors.