Data for research article: Horses form lasting impressions of people based on facial expressions of emotion during a single encounter.

Data for paper appearing in Current Biology March 2018Data files relating to the two phases of our experiment. Abstract from articleFor humans, facial expressions are important socialsignals, and how we perceive specific individualsmay be influenced by subtle emotional cues thatthey have given us in past encounters. A wide rangeof animal species are also capable of discriminatingthe emotions of others through facial expressions[1–5], and it is clear that remembering emotional experiences with specific individuals could have clearbenefits for social bonding and aggression avoidancewhen these individuals are encountered again.Although there is evidence that non-human animalsare capable of remembering the identity of individualswho have directly harmed them [6, 7], it is notknown whether animals can form lasting memoriesof specific individuals simply by observing subtleemotional expressions that they exhibit on theirfaces. Here we conducted controlled experimentsin which domestic horses were presented with aphotograph of an angry or happy human face andseveral hours later saw the person who had giventhe expression in a neutral state. Short-term exposureto the facial expression was enough to generateclear differences in subsequent responses to thatindividual (but not to a different mismatched person),consistent with the past angry expression havingbeen perceived negatively and the happy expressionpositively. Both humans were blind to the photographthat the horses had seen. Our results provideclear evidence that some non-human animals caneffectively eavesdrop on the emotional state cuesthat humans reveal on a moment-to-moment basis,using their memory of these to guide future interactionswith particular individuals.