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If you ever get the impression that your dog can "tell" whether you look content or annoyed, you may be onto something. Dogs may indeed be able to discriminate between happy and angry human faces, according to a new study.
Researchers trained a group of 11 dogs to distinguish between images of the same person making either a happy or an angry face. During the training stage, each dog was shown only the upper half or the lower half of the person's face.
The investigators then tested the pups' ability to discriminate between human facial expressions by showing them different images from the ones used in training. The dogs were shown either the other half of the face used in the training stage, the other halves of people's faces not used in training, a face that was the same half as the training face but from a different person, or the left half of the face used in the training stage.
The researchers found that the dogs were able to pick the angry or happy face by touching a picture of it with their noses more often than one would expect by random chance.
The study showed the animals had figured out how to transfer what they learned about human faces during training to new faces in the testing stage, the researchers said. [10 Things You Didn't Know About Dogs]
"We can rule out that the dogs simply discriminated [between] the pictures based on a simple salient cue, such as the visibility of teeth," said study author Corsin Müller, an animal behavior researcher at Messerli Research Institute at the University of Veterinary Medicine in Vienna.
"Instead, our results suggest that the successful dogs realized that a smiling mouth means the same thing as smiling eyes," and the same rule applies to an angry mouth having the same meaning as angry eyes, Müller said. (The researchers originally recruited 24 dogs for the study, but 13 of them dropped out for various reasons before the researchers started training them, for instance, because their owners did not have time to bring the animals to the lab.)
The study was published Thursday (Feb. 12) in the journal Current Biology.