Researchers at the University of Bristol discovered that dogs' behavior changes in response to a distinctive odor of stress that emanates from humans' sweat and breath. The research team enlisted 18 pairs of humans and dogs to participate in a series of experiments.
The researchers placed a food bowl containing treats in one location, while placing a similar empty bowl in another. Once the dogs learned the difference between these locations, they were quicker to approach the bowl with treats compared to the empty bowl. When a third bowl was introduced in a new location, the researchers measured the time it took for the dog to go to this location to explore; speed indicated optimism about the presence of a reward, while hesitation to explore the new bowl indicated pessimism.
During the experiment, the dogs completed the same test while exposed to the sweat odors and breath samples taken from humans who were not their owners. These odors were collected while participants were relaxed and listening to audio clips, as well as during stressful situations, such as completing a math test.
The researchers found that the dogs exposed to stress-related odors were less likely to check the third bowl, regardless of its location. Subsequent experiments also showed that dogs improved gradually in learning to identify the bowl locations and distinguished between them more quickly when exposed to stress odors.
The lead author of the study, Dr. Zoe Parr Curtis, told MailOnline: "Dogs have evolved alongside humans for thousands of years. This makes dogs susceptible to a phenomenon called 'emotional contagion,' where they pick up on their owners' mood."
Dogs may have developed this "pessimistic response" to human stress in order to conserve energy and avoid disappointment. The researchers believe this discovery could help professional dog trainers and owners understand how their emotions affect dog training. They expressed a desire to study the effects of emotions, such as happiness or deep relaxation, on dogs' mood as well.
