My dog can tell how I'm feeling, many owners say. According to a recent study, this could have something to do with the four-legged friend's keen sense of human well-being: The experiments show that dogs can distinguish between odor samples from relaxed and slightly stressed people. The findings shed further light on the complex animal-human relationship and could benefit the training of therapy dogs, the researchers say.
For us, seeing and hearing are in the foreground - but for man's "best friend" the sense of smell plays a comparatively important role in perception as is well known: The sensitivity of the dog's nose is legendary. In recent years, researchers have even shown the medical potential of sniffer dogs: they can detect various human diseases by smell. The animals perceive volatile organic compounds that the body releases under the special circumstances.
Previous studies have also provided evidence that the animals can smell emotional states of humans. For example, it has been shown that they react to odor samples from fearful situations with conspicuous behavior. The researchers led by Clara Wilson from Queen's University Belfast now wanted to underpin these findings and the subjective experiences of holders with a clearer experimental approach. It is based on a concept that is also used to detect diseases through the sense of smell in dogs.
On the trail of experimental stress
For the study, the researchers collected breath and sweat samples from 36 volunteers. They were taken both before and after an experiment that is often used in research into the induction of mild stress: the subjects were asked to perform mental arithmetic tasks under time pressure. In order to provide physiological evidence of the emotional stress caused by this, in addition to the personal assessments of the study participants, the pulse rate and blood pressure were recorded. Only the samples from subjects in whom these values had increased significantly were then used further in the study.
First, Wilson and her colleagues used rewards to train four dogs of different breeds to distinguish the stress samples from blanks without breath or sweat and to indicate the correct sample container. In phase two, each animal was presented with the stress sample, the same participant's stress-free sample, and a blank in a series of test vessels. From these three different categories, "Treo", "Fingal", "Soot" and "Winnie" should then sniff out the stress test correctly again.
People smell stressed
As the scientists report, the test animals were able to master these differentiating tasks with ease: in a total of 720 test runs, the dogs were correct on average around 94 percent of the time. The individual hit rate of the individual animals was 90 to 97 percent. The results thus show that the physiological processes associated with a stress response cause changes in the volatile organic compounds in human sweat or in the air we breathe that can be detected in dogs, the researchers conclude. Apparently, a comparatively low level of stress is sufficient for this. "And this is also true when dealing with people who are unknown to the dogs, as in our experimental approach," says Wilson.
The results now contribute to the understanding of the human-dog relationship and could also have practical significance, the researchers say: they could be used in the evaluation and training of therapy dogs, which are intended to provide emotional support to people with impairments such as post-traumatic stress disorder (PTSD). . "This is the first study of its kind to show that dogs don't need visual or auditory cues to sense human stress. That they are able to detect the condition based on olfactory cues alone could be useful information for their therapeutic use," says Wilson.
Source: Queen's University Belfast, Article: PLoS ONE, doi: 10.1371/journal.pone.0274143