Are we underestimating animals? After a recent study showed that ravens are aware of the consciousness of others, a team of researchers from the University of Sussex has now shown that horses can read human facial expressions - in particular, they can distinguish between angry and happy expressions.
The team examined 28 horses and gauged their reactions to the photographs of both positive and negative human facial expressions. After viewing angry faces, horses tended to look more with their left eye, a behavior previously shown to be associated with the perception of negative stimuli. Furthermore, their heart rate increased at a faster rate and they exhibited more stress-related behaviors.
The team believes that these response and physiological reactions indicate that horses understand the angry faces that they see. In fact, prior to this study, no other study has found a relationship between facial expressions and heart rate in human-animal interactions.
"What's really interesting about this research is that it shows that horses have the ability to read emotions across the species barrier," Amy Smith, who co-led the research, said in a press release. "We have known for a long time that horses are a socially sophisticated species, but this is the first time we have seen that they can distinguish between positive and negative human facial expressions."
Previous research found that many animal species view negative events with their left eye due to the brain's right hemisphere, which processes information from the left eye, specializing in the processing of threatening stimuli.
"It's interesting to note that the horses had a strong reaction to the negative expressions but less so to the positive," added Smith. "This may be because it is particularly important for animals to recognize threats in their environment. In this context, recognizing angry faces may act as a warning system, allowing horses to anticipate negative human behavior such as rough handling."
"There are several possible explanations for our findings," said Karen McComb, the other lead co-author of the study. "Horses may have adapted an ancestral ability for reading emotional cues in other horses to respond appropriately to human facial expressions during their co-evolution."
However, she also adds that it could stem from individual horses learning to interpret human emotion throughout the course of their lives.
"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," she said.
The findings were published in the Feb. 10 issue of Biology Letters.
