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Olfactory-based Interspecific Recognition of Human Emotions

Contributed by Dr. Jo

Sabiniewicz A, Tarnowska K, Świątek R, Sorokowski P, Laska M (2020) Olfactory-based interspecific recognition of human emotions: Horses (Equus ferus caballus) can recognize fear and happiness body odour from humans (Homo sapiens). Applied Animal Behaviour Science 230: 105072 https://doi.org/10.1016/j.applanim.2020.105072

Recognising the emotional state of other individuals within the same species is considered to be highly adaptive, after all if they are expressing negative emotions such as fear approaching them might not be a good idea, and you may be in danger yourself. Equally, if they are in a positive emotional state your approach might be welcomed and you might have the opportunity to engage in positive interactions such as mutual grooming or play. The benefits of being aware of the emotions expressed by individuals of other species can also be understood from a survival perspective, for example if you are hunted by the same predator understanding the warning cries and escape behaviours of other species around you may save your life.

There is growing evidence that some of our domestic animals can recognise human emotional state. Much of this research has been undertaken in dogs and horses and tends to use visual or auditory indicators of emotion, such as angry faces and happy voices. That our domestic animals can recognise our emotions is not entirely surprising. Most of us who live with and care for animals have examples of when they have responded to our emotional state. From the animal’s perspective, our emotions often have consequences for the way we handle and treat them. This being the case, having an ability to recognise our emotional state and so predict our behaviour is a useful skill to have.

People who spend their time around animals are usually very aware of the impact their behaviour can have on their animal companions. As equestrians, most of us learn early on to leave our daily stresses and frustrations behind when we go to our horses. But even if we can control our outward behaviour (or feel as if we do), our horses often pick up on how we feel.

This research study investigated whether horses are able to distinguish between human emotional state by smell alone, with no visual or auditory cues present. The odours of ten people were collected on cosmetic pads when they were happy or scared (both emotions generated by watching videos) and were presented to 21 horses alongside unused cosmetic pads serving as a control, and the behavioural responses of the horses were recorded. For each of the test conditions (odours of fear and happiness), samples of cosmetic pads used by four different people were presented to the horse together to minimise the effect of individual differences between the human odour donators. Testing happened in the horses stable in the presence of an unfamiliar researcher and a person familiar to the horse.

The researchers found some differences in the behavioural responses of the horses when presented with the two different odours and the control. There was a lot of variation between the individual horses in how they responded, which may reflect differences in their sensitivity and reactivity. These differences meant that many of the behavioural affects seen were not significant, however, they do suggest some recognition of human emotional state. Interestingly, the behavioural responses to the fear odour and the control were similar. The horses tended to lift their heads more often and for longer when they were presented with the fear odour and the control pad than they did when presented with the happiness odour. Horses also tended to touch the familiar person in the stable more often when presented with the fear odour. There were differences in ear movement between the three conditions, with horses keeping their ears back more when presented with the control odour, perhaps because they were more focused on environmental cues in the absence of relevant olfactory information. Interestingly, flehmen responses occurred infrequently, and when they were displayed, they were not directed towards the humans or the cosmetic pads.

As is often the case, the findings of this study were not clear cut and are open to interpretation – but that is how scientific research often goes. Yet they do suggest that horses are able to distinguish between olfactory indicators of human emotion, something that had previously only been shown in dogs. More research is needed to explore this further.

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