title: Perception of emotional valence in horse whinnies.
abstract: BACKGROUND
  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. 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  Horses 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.
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Elodie F
authors.initials: EF
authors.lastname: Briefer
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.|Koret School of Veterinary Medicine, Robert H. Smith Faculty of Agriculture, Food and Environment, the Hebrew University, Rehovot, 76100 Israel.
authors.forename: Roi
authors.initials: R
authors.lastname: Mandel
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.|Division of Animal Welfare, Veterinary Public Health Institute, Vetsuisse Faculty, University of Bern, Länggassstrasse 120, 3012 Bern, Switzerland.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Maigrot
authors.affiliation: Agroscope, Swiss National Stud Farm, Les Longs Prés, 1580 Avenches, Switzerland.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Briefer Freymond
authors.affiliation: Agroscope, Swiss National Stud Farm, Les Longs Prés, 1580 Avenches, Switzerland.
authors.forename: Iris
authors.initials: I
authors.lastname: Bachmann
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Edna
authors.initials: E
authors.lastname: Hillmann
keywords: Emotion expression; Emotional contagion; Equus caballus; Familiarity; Playbacks; Vocalisations