Research just published from the University of Sussex demonstrates that domestic horses use a sophisticated cognitive system to identify individuals of species other than their own.
Drs Leanne Proops and Karen McComb, of the School of Psychology's Mammal Vocal Communication and Cognition Research Group, had already shown that horses can combine auditory and visual information to recognise each other.
In their latest research they demonstrated that horses also use this system to distinguish between the different humans they know.
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 cross-modally.
“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 study was carried out using domestic horses that were accustomed to several different handlers.
Firstly the researchers 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 found that the horses responded more quickly and looked for longer and more often at the familiar human compared with the stranger when played their voice. They were significantly 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).
The researchers then tested how the horses would perform the more complex task of distinguishing between two familiar voices.
This time, the horses were able to match a specific familiar voice to its human handler. This indicates, say the researchers, that the sight of the handler activated a multi-modal memory of that specific individual, allowing each horse to match the sight of a particular person with the sound of their voice.
Horses likely use this recognition strategy naturally to identify numerous individual people in their day-to-day lives.
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