London, Feb 10: Horses can read human facial expressions and distinguish between happy and angry faces, scientists have found for the first time. Psychologists studied how 28 horses reacted to seeing photographs of positive versus negative human facial expressions.
When viewing angry faces, horses looked more with their left eye, a behaviour associated with perceiving negative stimuli.
Their heart rate also increased more quickly and they showed more stress-related behaviours. The study concludes that this response indicates that the horses had a functionally relevant understanding of the angry faces they were seeing.
The effect of facial expressions on heart rate has not been seen before in interactions between animals and humans.
"What's really interesting about this research is that it shows that horses have the ability to read emotions across the species barrier," said Amy Smith, a doctoral student at the University of Sussex who co-led the research.
"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," said Smith.
"The reaction to the angry facial expressions was particularly clear - there was a quicker increase in their heart rate, and the horses moved their heads to look at the angry faces with their left eye," she said.
Research shows that many species view negative events with their left eye due to the right brain hemisphere's specialisation for processing threatening stimuli (information from the left eye is processed in the right hemisphere).
"It's interesting to note that the horses had a strong reaction to the negative expressions but less so to the positive," Smith said.
"This may be because it is particularly important for animals to recognise threats in their environment. In this context, recognising angry faces may act as a warning system, allowing horses to anticipate negative human behaviour such as rough handling," she said.
A tendency for viewing negative human facial expressions with the left eye specifically has also been documented in dogs. "There are several possible explanations for our findings.
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," Professor Karen McComb, a co-lead author of the research, said.
The study was published in the journal Biology Letters.