Horses discriminate between emotion in human vocalization
In social species, vocalisation is important in promoting effective communication. Species with frequent human contact may benefit from interpreting human vocalisations and adjusting their behaviour accordingly.
Similar acoustic rules within vocalisations can be found across humans and non-human species. Harsh, low-frequency sounds are usually threatening, whilst higher, pure-tone frequencies tend to be used in appeasement or affiliative situations. For domestic species it would be even more advantageous to discriminate between negative and positive human voices, as has been proven to be true for dogs. The aim of the study was to investigate if horses discriminate between positive and negative emotion in human nonverbal vocalisations.
The study was executed by using playbacks of auditory stimuli to thirty-two horses. The vocalisations were male and female and characterised as either happy (laughter) or angry (growling). Each horse was presented with one positive and one negative stimuli separated by at least one week, either male or female but not both.
The results show that horse show a freeze posture significantly longer after hearing negative voices. In addition, with negative voices horses held their ears forward longer and moved their ears less, all vigilant behaviours.
Expert opinion by Anouk van Breukelen
The results give rise to more questions about the universality of vocal emotions in different species and are interesting for future research about the parameters that cause this discrimination.
> From: Smith et al., Nature Scientific Reports 8 (2018) 13052. All rights reserved to Creative Commons Attribution 4.0 International. Click here for the online summary.