Fluffy really does know what that big grin or frustrated frown on your face means.
At least, that's according to a new study that suggests dogs can tell from a facial expression whether a person is happy or angry. Scientists are calling the research -- which was published in the journal Current Biology on Feb. 12, 2015 -- the first solid evidence that humans aren't the only ones who can recognize emotional expressions in another species.
"Our study demonstrates that dogs can distinguish angry and happy expressions in humans, 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," study co-author Dr. Ludwig Huber, head of the University of Veterinary Medicine, Vienna's Messerli Research Institute in Austria, said in a written statement.
For the study, 11 dogs--including border collies, a fox terrier, a golden retriever, a German shepherd, and some mutts--were trained to discriminate between images of the same person making either an angry or happy face, National Geographic reported.
Some dogs were rewarded with a treat for picking out the happy face while others were rewarded for picking out the angry face, and some dogs were shown only the upper half of the face while others were shown only the lower half.
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The experimental set-up used to test whether dogs can recognize emotional expressions in human faces.
Then, in a series of four experiments, the researchers tested the dogs' facial expression-detecting abilities by showing them slightly different images than the ones they were trained on. For instance, the dogs were shown the same half of the face they were trained on but with a different person in the image, or they were shown the other half of the face they were trained on, among other variations. Just check out the video above to see one of the dogs in an experiment.
What did the researchers find? The dogs discriminated between the two facial expressions more often than chance would predict. The dogs who were rewarded for picking out happy faces during training learned this discrimination faster than dogs rewarded for angry faces, but that could have been a result of many dogs (and many people for that matter) having negative associations and memories attached to angry faces, according to the researchers.
"This new work continues to build the case for just how sensitive dogs are to our subtle behaviors," Dr. Brian Hare, an associate professor at Duke University, who was not involved in the study, told the Los Angeles Times in an email. "This is the strongest evidence yet that dogs may even read our facial expressions."
This isn't the first time that scientists have noticed a canine's ability to "read" emotion in human faces. In 2012, a study showed that dogs can read human expressions as well as human infants can. And a 2008 study suggested that our canine companions can see at a glance if we are happy, sad, angry or pleased.
Woof to that!