Researchers at the University of Veterinary Medicine Vienna demonstrated that dogs can discriminate between happy and angry human faces, most likely by recalling real human faces to accomplish the task. The study was published on Feb. 12 in Current Biology.

"Our study demonstrates that dogs can distinguish angry and happy expressions in humans," research author Ludwig Huber told the BBC. "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."

According to Science Daily, the research team divided 20 dogs into two groups. The dogs faced a touch screen and viewed photos of happy and angry women’s faces side by side. The dogs also viewed images split horizontally so that only the eye or mouth regions of the human faces were visible. (This way, the dogs wouldn’t pick up subtle differences in the photos such as frown lines.) One group of dogs was rewarded for repeatedly choosing happy faces, and the other group for selecting angry faces. The machine dispensed treats based on the task assigned to the dog.

The study also found that dogs who were rewarded for recognizing happy faces did so more quickly than the group of dogs rewarded for recognizing angry faces, a likely reaction if the dogs believed the angry faces to be aversive.

Photo: Copyright Clever Dog Lab, Messerli Research Institute, Vetmeduni Vienna