Only slight changes to the way we say something can give it a positive or a negative spin. Can the same be said of horse whinnies?
Scientists have examined this very question in a study carried out in Switzerland.
Researchers investigated what they called separation and reunion whinnies, and in particular how the response to the latter varied when it involved familiar and unfamiliar horses.
The findings of Elodie Briefer and her colleagues on their exploration of what they described as the emotional valence of whinnies have been reported in the journal Frontiers of Zoology.
The study team set up an experiment in which they measured the physiological and behavioural reactions to whinnies recorded during emotionally negative situations (social separation) and positive situations (social reunion).
They used 18 horses of various breeds housed at five different farms.
Each was exposed to four playback treatments:
- Separation whinnies from a familiar horse;
- Reunion whinnies from the same familiar horse;
- Separation whinnies from an unfamiliar horse; and
- Unfamiliar reunion whinnies from the same unfamiliar horse.
During the playbacks, the horses were monitored for five behavioural parameters (locomotion, head movement and position, chewing, vocalisation and time to react); and three physiological parameters (inter-heart-beat interval [heart rate], respiration rate and skin temperature).
The horses reacted differently − in terms of respiration rate, head movements, the height they held their head and the time to respond − to separation and reunion whinnies when produced by familiar horses, but not with unfamiliar individuals.
They were also more emotionally aroused, with shorter inter-pulse intervals and more movement, when hearing unfamiliar compared to familiar whinnies.
“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,” they concluded.
Horses perceived acoustic cues within whinnies, both in terms of the emotional tone and familiarity, they concluded.
“These two graded whinny variants could constitute functionally distinct calls, increasing the horses’ potential to transmit information and enable fine-tuned communication between individuals within a given situation,” they wrote.
Discussing their findings, they said it was unclear whether contagion of emotional valence occurred.
“However, our study shows that horses are capable of perceiving variation in vocal parameters indicating emotional valence within whinnies.
“To our knowledge, 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.”
Affective prosody is the element of speech that contains emotional as well as linguistic information.
Interestingly, horses’ behaviour and physiology significantly differed between playbacks of separation and reunion whinnies when these sounds were produced by familiar individuals, but not when produced by unfamiliar ones.
This, they said, suggested better perception of emotional valence in familiar compared to unfamiliar whinnies.
The study team had already shown in previous research that whinnies are constituted by two fundamental frequencies, and that those produced during social separation were longer and had a higher frequency than those produced during social reunions.
Separation and reunion whinnies were therefore acoustically graded variants of the same call type.
The study team comprised Briefer Roi Mandel, Anne-Laure Maigrot, and Edna Hillmann, all from the Institute of Agricultural Sciences in Zurich; and Sabrina Briefer Freymond and Iris Bachmann, both from Agroscope, the Swiss National Stud Farm, in Les Longs Prés.
Perception of emotional valence in horse whinnies
Elodie F. Briefer, Roi Mandel, Anne-Laure Maigrot, Sabrina Briefer Freymond, Iris Bachmann and Edna Hillmann
Frontiers in Zoology 2017 14:8 DOI: 10.1186/s12983-017-0193-1