There has often been debate about how the domestication of animals and our behaviour around them might have changed their abilities. Various studies have been undertaken in an attempt to understand how animals interpret their human companions: Can they distinguish between human emotions?
Well your equine friend isn’t going to recognise you’re having a bad day and make you a nice cup of tea but according to a new study from a Mammal Vocal Communication and Cognition research group from the University of Sussex tests have shown for the first time that they could “spontaneously discriminate between positive (happy) and negative (angry) human expressions in photographs”.
What does this mean? Domestic horses can recognise that you are angry from your facial expression.
Mammal brains have a lateralized response system, with stimuli from the left eye being processed by the right hemisphere of the brain and stimuli from the right eye being processed by the left hemisphere of the brain. Further more it has been noted that there is often a system of hemispheric biases within the mammal brain regarding environmental stimuli: The right hemisphere specialises in processing “negative valenced” stimuli such as agonistic encounters. Thus negative input would be viewed with a “left-gaze bias”. In turn, the left hemisphere could have specialised in processing positive encounters, but evidence here is debated. For example a study in 2015 using dogs confirmed that negative visual input was viewed with a “left-gaze bias” but positive input did not demonstrate a “right-eye bias” (Muller, 2015).
In the team’s study the “left-eye bias” was used to evaluate responses to stimuli and classify this response as “negative” or “positive”. Objective insight was provided by monitoring the horse’s heart rate. Behavioural responses such as gaze duration, approach and avoidance durations were also observed.
28 horses for five riding and livery stables in Sussex were used in the behavioral analysis with a further 17 being used to establish mean heart rate and heart recovery rates. The “stimuli” were A3 colour photographs to two male individuals, unknown to the horses. There were 4 photos used: 2 with “angry” negative expressions, 1 of each model and 2 “happy” positive expressions, also 1 of each model.
It was observed that when viewing the negative stimuli, more horses looked left for their first gaze rather than right. To add to this there was a left-gaze bias in total looking time. Heart rate also was significantly higher when exposed to the negative rather than the positive stimuli. This suggests that the horses recognised that the angry expression was negative input and reacted accordingly.
No laterality was observed in responses to positive stimuli, concurring with the findings of the prior studies of canine responses.
The findings suggest that domestic horses can indeed recognize and respond “in a functionally relevant way” to human facial expressions of anger. This behavior could have been acquired as a species since domestication due to extensive exposure to human emotional responses and necessary responses to evolutionary pressure. It also could have evolved from an ancestral ability to understand members of the same species, having being transferred to a completely different species. Other people note that this behavior could be mostly acquired during the individual’s lifetime and responses are thus different depending on whether the individual is known to the horse or not. Once again studies of dogs provide an insight, suggesting that dogs perform better when faced with an individual they know. This could prove true to horses also.
Muller. C.A, Schmitt. K, Barber, A.L.A, Huber. L (2015) “Dogs Can Discriminate Emotional Expressions of Human Faces” Current Biology (25), 5: 601-605
Smith. A. V, Proops. L, Grounds. K, Wathan. J, McComb. K (2016) “Functionally relevant repsonses to human facial expressions of emotion in the domestic horse (Equus caballus)” Biology Letters (12)
Full article available here: http://rsbl.royalsocietypublishing.org/content/roybiolett/12/2/20150907.full.pdf
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