Abstract
BackgroundNon-human animals often produce different types of vocalisations in negative and positive contexts (i.e. different valence), similar to humans, in which crying is associated with negative emotions and laughter is associated with positive ones. However, some types of vocalisations (e.g. contact calls, human speech) can be produced in both negative and positive contexts, and changes in valence are only accompanied by slight structural differences. Although such acoustically graded signals associated with opposite valence have been highlighted in some species, it is not known if conspecifics discriminate them, and if contagion of emotional valence occurs as a result. We tested whether domestic horses perceive, and are affected by, the emotional valence of whinnies produced by both familiar and unfamiliar conspecifics. We measured physiological and behavioural reactions to whinnies recorded during emotionally negative (social separation) and positive (social reunion) situations.ResultsWe show that horses perceive acoustic cues to both valence and familiarity present in whinnies. They reacted differently (respiration rate, head movements, height of the head and latency to respond) to separation and reunion whinnies when produced by familiar, but not unfamiliar individuals. They were also more emotionally aroused (shorter inter-pulse intervals and higher locomotion) when hearing unfamiliar compared to familiar whinnies. In addition, the acoustic parameters of separation and reunion whinnies affected the physiology and behaviour of conspecifics in a continuous way. However, we did not find clear evidence for contagion of emotional valence.ConclusionsHorses are thus able to perceive changes linked to emotional valence within a given vocalisation type, similar to perception of affective prosody in humans. Whinnies produced in either separation or reunion situations seem to constitute acoustically graded variants with distinct functions, enabling horses to increase their apparent vocal repertoire size.
Highlights
Non-human animals often produce different types of vocalisations in negative and positive contexts, similar to humans, in which crying is associated with negative emotions and laughter is associated with positive ones
We analysed three physiological and five behavioural parameters that were previously shown to be affected by emotional valence and/or arousal [24], in addition to the latency of the subjects to respond to the playbacks (Table 1)
This is the first demonstration of perception of changes linked to emotional valence within a given vocalisation type in a non-human species, and is similar to perception of affective prosody in humans
Summary
Non-human animals often produce different types of vocalisations in negative and positive contexts (i.e. different valence), similar to humans, in which crying is associated with negative emotions and laughter is associated with positive ones. Some types of vocalisations (e.g. contact calls, human speech) can be produced in both negative and positive contexts, and changes in valence are only accompanied by slight structural differences. Such acoustically graded signals associated with opposite valence have been highlighted in some species, it is not known if conspecifics discriminate them, and if contagion of emotional valence occurs as a result. Short-lived affective reactions to specific events or stimuli They can be characterised using two main dimensions (dimensional approach): valence (negative/unpleasant or positive/pleasant) and arousal (bodily activation or excitation; e.g. calm versus excited) [1]. If this signal is positive, it could trigger a change in emotional valence from negative or neutral to positive
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