Do you think horses recognize each other as individuals? Research from the Proceedings of the National Academy of Sciences of the United States of America (PNAS) was published in 2009 and the full text of the research is now available online.
The research looked at whether horses would recognize a vocalization from a known vs unknown horse after a known horse was taken out of sight of a herd. The title of this article is, "Cross-modal individual recognition in domestic horses (Equus caballus."
Individual recognition is considered a complex process and, although it is believed to be widespread across animal taxa, the cognitive mechanisms underlying this ability are poorly understood. An essential feature of individual recognition in humans is that it is cross-modal, allowing the matching of current sensory cues to identity with stored information about that specific individual from other modalities. Here, we use a cross-modal expectancy violation paradigm to provide a clear and systematic demonstration of cross-modal individual recognition in a nonhuman animal: the domestic horse. Subjects watched a herd member being led past them before the individual went of view, and a call from that or a different associate was played from a loudspeaker positioned close to the point of disappearance. When horses were shown one associate and then the call of a different associate was played, they responded more quickly and looked significantly longer in the direction of the call than when the call matched the herd member just seen, an indication that the incongruent combination violated their expectations. Thus, horses appear to possess a cross-modal representation of known individuals containing unique auditory and visual/olfactory information. Our paradigm could provide a powerful way to study individual recognition across a wide range of species.
Leanne Proops, Karen McComb and David Reby designed the research; Proops performed research and analyzed data; all three wrote the paper. The researchers are from the Centre for Mammal Vocal Communication Research, Department of Psychology, School of Life Sciences, University of Sussex, United Kingdom. The paper was edited by Jeanne Altmann, Princeton University, Princeton, N.J.