Are you happy? Your dog can tell.
Dog owners may think their pets can tell a smile from a frown, but scientific evidence has been lacking.
Now, researchers have trained dogs from a variety of breeds to look at a pair of photos arranged side by side—one showing the upper half of a woman’s face looking happy and the other showing the upper half of the same woman’s face looking angry—and pick out the happy expression by touching their snouts to it (pictured).
When then shown the lower halves of the faces or pieces of other people’s faces, the perceptive pooches could still easily discern happy from angry. Another group of canines similarly learned to identify angry faces.
Dogs in a previous study that distinguished expressions on whole faces could have done so using simple visual clues that reappeared in every face: the white of teeth in a smile, for instance, or creases in angry skin.
Identifying emotions from photos of different parts of the face requires a more holistic understanding of expression, argue the authors of the new study. While primates are known to recognize faces, dogs may have been especially adapted for emotional sensitivity to humans during their domestication. The researchers plan to investigate how common this ability is by testing pigs and other animals.
Highlights
· We demonstrate that pet dogs can discriminate emotional expressions in human faces
· We can rule out that discrimination was based on simple local cues
· This ability may depend on extensive interaction with humans and/or domestication
· Dogs probably use their memories of real emotional human faces to accomplish the task
Müller CA, Schmitt K, Barber ALA, Huber L. Dogs Can Discriminate Emotional Expressions of Human Faces. Current Biology. 2015. http://www.cell.com/current-biology/abstract/S0960-9822(14)01693-5
The question of whether animals have emotions and respond to the emotional expressions of others has become a focus of research in the last decade. However, to date, no study has convincingly shown that animals discriminate between emotional expressions of heterospecifics, excluding the possibility that they respond to simple cues. Here, we show that dogs use the emotion of a heterospecific as a discriminative cue.
After learning to discriminate between happy and angry human faces in 15 picture pairs, whereby for one group only the upper halves of the faces were shown and for the other group only the lower halves of the faces were shown, dogs were tested with four types of probe trials:
(1) the same half of the faces as in the training but of novel faces,
(2) the other half of the faces used in training,
(3) the other half of novel faces, and
(4) the left half of the faces used in training.
We found that dogs for which the happy faces were rewarded learned the discrimination more quickly than dogs for which the angry faces were rewarded. This would be predicted if the dogs recognized an angry face as an aversive stimulus.
Furthermore, the dogs performed significantly above chance level in all four probe conditions and thus transferred the training contingency to novel stimuli that shared with the training set only the emotional expression as a distinguishing feature.
We conclude that the dogs used their memories of real emotional human faces to accomplish the discrimination task.