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Study: Dogs Can Recognize Human Emotional Expressions

A dog considers which face is happy, and which is angry. (Anjuli Barber, Messerli Research Institute)

So, you think you know your dog. But how well does your dog know you? She probably recognizes you when she sees you, but can the dog tell by simply looking at you whether you have a happy or an angry expression on your face? Researchers have taught pet dogs to know the difference.

Dogs are very attuned to sound. When they yell or speak harshly, many owners claim their dogs act guilty and slink away. But researchers in Austria have discovered that dogs can look at our faces, and tell the difference between a smile and a scowl.

In a series of experiments, researchers at the University of Veterinary Medicine Vienna taught dogs to recognize facial expressions by training them with two pictures of either the upper or lower half of a person's face, one happy, the other angry.

Then, the canines were shown images of the eyes or mouths of people they had never seen before, as well as the left half of the faces used in training.

Corsin Muller led the study.

“We were asking essentially, do they realize that smiling eyes have the same meaning as a smiling mouth, or angry eyes have the same meaning as an angry mouth? And it turned out that they really did perform very well in these probe trials. So, once they had learned the initial discrimination, they could spontaneously, immediately choose the correct one in the probe trials with the normal stimuli," said Muller.

In other words, once the dogs learned to recognize which image was happy or angry, they could easily identify the same expressions in pictures of any faces.

Muller says future work will try to determine whether dogs can learn the meaning of certain expressions - for example, whether a scowl indicates a person is angry.

“What we can say with our study is that they can discriminate them, that they can tell these ones are different. What we cannot be sure of at this point is what exact meaning they are associating with these different expressions. It seems of course likely that they would associate some positive meaning with the smiley face and they would associate some rather negative meaning with the angry face. But what exactly they are associating with these expressions we cannot know at this point," he said.

In the training trials, researchers found the dogs were slower to associate a reward with recognition of the angry face, suggesting they had an idea people with angry faces were best avoided.

Muller says canine investigators are also interested in finding out whether wild wolves can be trained to recognize human facial expressions.

The findings, published in the journal Current Biology, provide the first solid evidence that we are not the only species that can read another species' body language.