Humans have domesticated many kinds of animals in their history. Dogs and horses have particularly close relationships with humans as cooperative partners. However, fewer scientific studies have been conducted on cognition in horses compared to dogs. Studies have shown that horses cross-modally distinguish human facial expressions and recognize familiar people, which suggests that they also cross-modally distinguish human emotions. In the present study, we used the expectancy violation method to investigate whether horses cross-modally perceive human emotions. Horses were shown a picture of a human facial expression on a screen, and they then heard a human voice from the speaker before the screen. The emotional values of the visual and auditory stimuli were the same in the congruent condition and different in the incongruent condition. Horses looked at the speaker significantly longer in the incongruent condition than in the congruent condition when they heard their caretaker’s voices but not when they heard the stranger voice. In addition, they responded significantly more quickly to the voice in the incongruent condition than in the congruent one. To the best of our knowledge, this is the first study to show that horses cross-modally recognized the emotional states of their caretakers and strangers.

Simple SummaryIt is important for social animals to be sensitive to others’ emotional cues, because they can process and react to valuable social and environmental information more efficiently if they can understand others’ emotional states. Such sensitivity also seems to be adaptive in animal communication with both conspecific and heterospecific individuals, particularly for dogs and horses, because these animals have been cooperating with humans since the advent of domestication. Previous studies have demonstrated that dogs are very sensitive to human cues, such as pointing and facial or vocal expressions. However, few studies have examined whether horses exhibit a sensitivity to human emotional cues that is comparable to dogs’ sensitivity. In this study, we investigated whether horses are sensitive to human emotional cues and adjust their behavior accordingly. The results revealed that human emotional cues influenced the frequency of gaze following and the amount of time that horses looked at humans. Horses avoided following the human gaze and looked in their direction for a shorter period of time when humans displayed expressions of disgust. These findings support our hypothesis that horses exhibit sensitivity to negative human emotional cues.AbstractEmotions are important for social animals because animals’ emotions function as beneficial cues to identify valuable resources such as food or to avoid danger by providing environmental information. Emotions also enable animals to predict individuals’ behavior and determine how to behave in a specific context. Recently, several studies have reported that dogs are highly sensitive to not only conspecific but also human emotional cues. These studies suggest that domestication may have affected such sensitivity. However, there are still few studies that examine whether other domesticated animals, in addition to dogs, exhibit sensitivity to human emotional cues. In this study, we used a gaze-following task to investigate whether horses (Equus caballus) are sensitive to human emotional cues (happy, neutral, disgust) and if they adjust their behavior accordingly. In the study, the experimenter suddenly turned her head to either right or left and showed emotional cues. The results revealed that horses significantly decreased the frequency with which they followed the experimenter’s gaze and the total looking time during the gaze-emotional cue presentation in the Disgust condition compared to the Neutral condition. These results suggest the possibility that horses are sensitive to human emotional cues and behave on the basis of the meaning implied by negative human emotional cues.

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