Feeling happy or mad? A dog can tell your mood just by looking at the expression on your face.
New research in the journal Current Biology represents the first solid evidence that an animal other than humans can discriminate between emotional expressions in another species.
As any dog owner knows, canines are skilled at figuring us out, but previously more attention was paid by scientists to how dogs read us using their other senses, such as smell and hearing, and by observing our behaviors. The latest study strongly suggests that the sight alone of a smile, frown, scowl and more conveys our moods to dogs.
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"We think the dogs in our study could have solved the task only by applying their knowledge of emotional expressions in humans to the unfamiliar pictures we presented to them," co-author Corsin Müller of the University of Veterinary Medicine Vienna said in a press release.
For the study, Müller and his team took photos of the same person making either a happy or an angry face. The researchers then showed the photos to dogs, which were trained to discriminate between the happy and angry expressions. The researchers then showed only the upper or lower halves of the images to the dogs, which lost none of their ability to discriminate.
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The researchers next presented the dogs with photos of different people making their own happy and angry expressions. Müller and his colleagues mixed up the images, sometimes showing the dogs one person or the other, or showing the upper or lower halves of the pictures.
The dogs were able to select the angry or happy face more often than would be expected by random chance in every case.
"Our study demonstrates that dogs can distinguish angry and happy expressions in humans," lead author Ludwig Huber of the University of Veterinary Medicine Vienna's Messerli Research Institute said. He added that "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."
He continued that "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."
Supporting this is the fact that dogs have a hard time learning to associate an angry human face with a reward, suggesting that they already know -- based on prior experience -- that mad people aren't likely to offer treats and head rubs.
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More studies are in the works to learn more about how dogs recognize human emotions. The researchers also plan to study how dogs themselves express different emotions, and how their feelings are influenced by those of their owners or other people.
"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," Müller said.
It could be that dogs are so close to humans that they understand us better than any other species. But maybe other pets, such as cats, understand our expressions too.
The answer to that remains unknown to science for now, but anecdotal evidence suggests that other animals can also read our moods with a brief glance.
Photo: The experimental set-up used to test whether dogs can discriminate emotional expressions of human faces. Credit: Anjuli Barber, Messerli Research Institute