While most dog owners are well aware that their pets are affected by their emotions, new research suggests human stress can actually lead dogs to make more “pessimistic” choices.
Dogs can smell human stress in the air, whether it’s from their owner or a stranger — and it impacts the kinds of decisions they make as well as their emotional state, according to a new study.
The small study, led by researchers at the University of Bristol and published in Scientific Reports, is the first of its kind to analyze the impact of the smell of human stress on dogs’ emotional state.
Previous research has suggested that when humans make “optimistic’” or “pessimistic” choices, their decisions are connected to positive or negative emotions, respectively. Researchers used this framework to test whether dogs would make “optimistic” or “pessimistic” choices when exposed to both stress odors and relaxation odors from humans, and to determine how their emotional state might be impacted.
A total of 18 dog-and-owner duos took part in the study. All the dogs were trained that a food bowl would contain a treat when it was placed in one specific location but would be empty in another specific location. After the dogs underwent this training, they approached the bowl in the location with the treat much quicker than the empty one.
Researchers then tested how quickly each dog would go to new bowl locations without knowing whether or not they’d contain a treat. Approaching the bowl quickly reflected an “optimistic” view that food would be present in the new locations and a positive emotional state, while a slower reaction meant a “pessimistic” response and negative emotional state.
The trials were all repeated with dogs being exposed to no odors, the odors of sweat and breath samples from unfamiliar stressed humans, and the odors of sweat and breath samples from unfamiliar relaxed humans.
Following the trials, the researchers concluded that the dogs were slower to approach the mystery bowls when they had been exposed to the stress odors, though this was not the case when exposed to the relaxed odors.
The authors suggest that the stress odors may have given the dogs a “pessimistic” view over whether the bowl would contain a treat and worsened their emotional state.
The study also found that repeating the tests improved the dogs’ ability to learn about the bowls throughout the trials and that the dogs actually learned more quickly when exposed to the stress smell. While this suggests that mild handler stress may actually improve working performance in dogs, the authors note that very high or chronic stress levels can lead to learning and memory impairment.
“Understanding how human stress affects dogs' wellbeing is an important consideration for dogs in kennels and when training companion dogs and dogs for working roles such as assistance dogs,” said lead researcher Nicola Rooney, senior lecturer in wildlife and conservation at Bristol Veterinary School, in a news release. “Dog owners know how attuned their pets are to their emotions, but here we show that even the odor of a stressed, unfamiliar human affects a dog’s emotional state, perception of rewards, and ability to learn.”
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