You walk by many different dogs and cats in an animal shelter, some look healthy, lively, and energetic. You see a dog in the corner of its pen looking sad and lonely. All this goes to show that you have the ability to distinguish emotions in another species. But does your animal share this ability? Do you know whether it's able to recognize when you're sad, happy, or angry? Recent science shows that it may indeed be possible...

Some people would say yes without hesitation, particularly longtime dog owners. It's difficult to put into words, but dogs know when we're sad or happy, and it's what makes human/dog relationships so special. Others might say just the opposite because, from the outside, it seems unlikely and probably due to a misperception related to a poor understanding of animal behavior, an idea grounded in a deep desire to communicate with our canine companions and not simply to act as their masters.

Researchers are also interested in answering this question because the exploration of both cognitive and behavior mechanisms is not a field of study that's exclusively restricted to humans. In this study, an Austrian team of scientists studied the ability of dogs to discriminate between different human facial expressions. For the purposes of this study, dogs were trained to choose between two emotions: joy and anger. The emotions were displayed by a person in a photograph, and dogs had to demonstrate the preference they had been trained on by touching one of the photographs with their noses. To make the task more interesting, the faces were cut in two so that the dogs could only see either the lower part (area around the mouth) or the upper part (area around the eyes) of the face. After this learning phase, the animals' ability to discriminate was tested in four different ways.

The first method involved showing the same part of the face they had seen during the training phase, but using a photo of a different person. The second method involved showing the other half of the face of the same person. In the third, the dogs saw the other part of the face of a new person. And finally in the fourth, they were presented with the left half of the face of the same person.

In each of these four situations, the dogs were able to select the expression they had been taught to recognize. They of course made some errors, but the results were well above chance. According to the authors' conclusions, dogs are not only able to learn and recognize human facial expressions, but can also transfer this ability to new faces.

It remains to be seen what meaning dogs attach to smiles or angry expressions, a question that may prove difficult to answer. Nevertheless, the researchers had a harder time teaching the dogs to associate a negative expression with a reward, which suggests that the dogs base their perception on past experience. "What exactly those different meanings are for the dogs is hard to say, 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," states Ludwig Huber, the senior author and head of the group at the University of Veterinary Medicine in Vienna.