Dogs can discriminate human emotional expressions, according to a new study carried out by scientists at the University of Veterinary Medicine in Vienna, Austria.
German Shepherd puppy. Image credit: Marilyn Peddle / CC BY 2.0.
“We think the dogs in our study could have solved the task only by applying their knowledge of emotional expressions in humans to the unfamiliar pictures we presented to them,” said Dr Corsin Müller, the first author of the study published in the journal Current Biology.
Previous attempts had been made to test whether dogs could discriminate between human emotional expressions, but none of them had been completely convincing.
In the new study, Dr Müller and his colleagues trained 20 dogs to discriminate between images of the same person making either a happy or an angry face.
To exclude the possibility that the animals were making their decisions based on conspicuous differences between the two pictures, such as teeth or frown lines, the researchers split the images horizontally so that during the training phase the dogs saw either only the eye region or only the mouth region.
After training on 15 picture pairs, the dogs’ discriminatory abilities were tested in four types of trials: (i) the same half of the faces as in the training but of novel faces, (ii) the other half of the faces used in training, (iii) the other half of novel faces, and (iv) the left half of the faces used in training.
The dogs were able to select the angry or happy face more often than would be expected by random chance in every case.
The findings show that not only could the dogs learn to identify facial expressions, but they were also able to transfer what they learned in training to new cues.
“It seems that dogs dislike approaching angry faces,” said study senior author Dr Ludwig Huber.
“We believe that dogs draw on their memory during this exercise. They recognize a facial expression which they have already stored,” Dr Müller added.
“We suspect that dogs that have no experience with people would perform worse or could not solve the task at all.”
Dr Huber said: “our study demonstrates that dogs can distinguish angry and happy expressions in humans, they can tell that these two expressions have different meanings, and they can do this not only for people they know well, but even for faces they have never seen before.”
“It is hard to say what exactly those different meanings are for the dogs, but it appears likely to us that the dogs associate a smiling face with a positive meaning and an angry facial expression with a negative meaning.”
The team reports that the dogs were slower to learn to associate an angry face with a reward, suggesting that they already had an idea based on prior experience that it’s best to stay away from people when they look angry.
The scientists plan to explore the role of experience in the dogs’ abilities to recognize human emotions. They also plan to study how dogs themselves express emotions and how their emotions are influenced by the emotions of their owners or other humans.
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