Horses share some surprisingly similar facial expressions to humans and chimps, according to University of Sussex researchers.
The findings, published in the Plos One journal, suggest evolutionary parallels in different species in how the face is used for communication.
The study builds on previous research showing cues from the face are important for horses to communicate.
Researchers developed an objective coding system to identify individual facial expressions on the basis of underlying muscle movement.
The Equine Facial Action Coding System (EquiFACS), as devised by the Sussex team in collaboration with researchers at the University of Portsmouth and Duquesne University, Pittsburgh, US, identified 17 “action units” (discrete facial movements) in horses. In comparison, there are 27 in humans, 13 in chimps and 16 in dogs.
The study’s co-lead author, doctoral researcher Jennifer Wathan, said: “Horses are predominantly visual animals, with eyesight that’s better than domestic cats and dogs, yet their use of facial expressions has been largely overlooked.”
“Despite the differences in face structure between horses and humans, we were able to identify some similar expressions in relation to movements of the lips and eyes” she added.
The researchers were surprised by the repertoire of complex facial movements in horses and how many of them were similar to humans. The next step is to look at how the expressions relate to emotional states.
Researchers analysed video footage of a wide range of naturally occurring horse behaviours to identify all the different movements it is possible for horses to make with their face. They also carried out an anatomical investigation of the facial muscles that underpin these movements. Each individual movement that was identified was given a code.
To read the paper in full, visit: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0131738