Dogs are able to differentiate between happy and angry faces in humans, representing the first kind of solid evidence that humans are not the only ones who can distinguish between expressions of emotions, according to a study.

Attempts have been made before to test whether or not dogs are able to tell the difference between emotional expressions in humans but none have been completely successful.

In a study published in the journal Current Biology, researchers set out to determine once and for all if dogs have the capabilities to tell emotional expressions apart by teaching canines to discriminate between a happy and an angry face.

The dogs were split into two groups, one assigned to learn happy faces while the other was given angry faces. In each training session, whether they belonged to the happy or angry face group, the dogs were shown only the upper or lower halves of faces.

After being trained with 15 pairs of pictures, the dogs were assessed following four types of tests: using the same halves of novel faces (faces not used during the training); using the same halves of training faces; using the other halves of novel faces; and using the other halves of training faces.

Results showed that dogs are capable of identifying happy or angry faces even in faces they have just seen (novel faces). This means that not only are dogs able to discriminate between emotional expressions, but they are also capable of applying what they have learned to new cues.

While the study demonstrates that dogs are capable of distinguishing between meanings, what these meanings are exactly for dogs remain unclear. It looks as though happy faces are associated with positivity, while angry faces are connected with negativity, since dogs appear to know that it is best to avoid an angry face.

Researchers are interested in carrying out further work into the canine ability to recognize emotions in humans, as well as exploring how dogs themselves express emotions, and how their emotions are affected by their human's or other people's emotions.

"We expect to gain important insights into the extraordinary bond between humans and one of their favorite pets, and into the emotional lives of animals in general," said Corsin Müller from the University of Veterinary Medicine Vienna, one of the authors of the study.

Other authors for the study include Ludwig Huber, Anjuli Barber and Kira Schmidt.

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