Dr Leanne Proops makes a friend of one of the horses

A new Sussex study published today (16 May) shows that domestic horses use a sophisticated cognitive system to identify individuals of species other than their own.

A previous study by the Mammal Vocal Communication and Cognition Research Group in the School of Psychology demonstrated that horses have the ability to combine auditory and visual information to recognise each other.

Now, in their paper published online by the Proceedings of the Royal Society B, Dr Leanne Proops and Dr Karen McComb have been able to show that horses also employ this system for distinguishing between the different humans they know. They also found that females were better at it than males.

Lead researcher Dr Proops said: “The domestic horse is an ideal animal model for this research because it has a complex social organisation and close relationship to humans, making individual recognition of humans a highly functional ability.”

Dr McComb explained: “When we hear a familiar voice we form a mental picture of who spoke. We match visual and auditory cues to recognise specific individuals. Previously we showed that horses also identify other horses.

“We now demonstrate how flexible this ability is by showing that horses can also recognise humans in this way, despite people looking and sounding very different to themselves.”

The researchers carried out their study on domestic horses that were accustomed to several different handlers.

They first tested where the horse would look when two voices - one familiar, one unfamiliar - were played from a hidden loudspeaker, either side of which stood the familiar and unfamiliar person.

They then tested how the horses would perform in the more complex task of having to distinguish between two familiar voices played to them that were from different handlers that they knew.

They found that the horses were faster to respond and looked for longer and more often at the familiar human compared with the stranger when played their voice, and were better at making this match when the familiar person was on the right of their visual field (indicating that the left hemisphere of the brain is involved in this processing).

In the second experiment, the horses proved able to match a specific familiar voice to its human handler. This indicated that the sight of the handler activated a memory of that specific individual, allowing each horse to match the sight of a particular person with the sound of their voice.

The results suggest the horses use this recognition strategy naturally to identify numerous individual people in their day-to-day lives.