By Maureen SalamonHealthDay Reporter

THURSDAY, Feb. 12, 2015 (HealthDay News) — Smiling? Frowning? New research indicates that dogs can tell the difference, though it’s still unclear whether they understand the emotions behind people’s facial expressions.

Austrian researchers found that dogs were able to distinguish between happy and angry expressions in humans — a feat the study authors contend was possible because the canines applied their knowledge of emotional expressions in humans to a set of unfamiliar pictures presented to them.

While the researchers said the study is the first such evidence that dogs — or any animal — can discriminate between human facial expressions, animal experts said it comes as no surprise.

“We think the bond between dogs and humans is even stronger and the communication abilities even more subtle than so far assumed — by many hard-core scientists, at least,” said study senior author Ludwig Huber, head of comparative cognition at the University of Veterinary Medicine in Vienna.

“We suggest, though this still needs more [research], that dogs learn from us, they feel like we do and maybe understand us better than we understand them,” Huber added.

For the study, Huber and his colleagues trained about a dozen dogs to discriminate between images of the same person making either a happy or angry face by showing them only the upper or lower half of the face.

After training with 15 pairs of images, the dogs’ abilities were tested in four ways. The canines were able to tell the difference between the happy and angry face more often than expected just by chance. This indicates they can tell the two expressions have different meanings, even in unfamiliar faces, Huber said.

“This does not mean that they understand the emotions,” he added. “We need further experiments to prove this.”

But while scientific confirmation awaits, U.S. veterinarians said their everyday contact with dogs shows they are capable of reading faces and interpreting underlying emotions.

“There’s a saying I use in the clinic: Your dog can read you like a book,” said Dr. Nicholas Dodman, a professor of animal behavior at Tufts University Cummings School of Veterinary Science in North Grafton, Mass. “They can read your body language, your eyes, your pupil size; I’m not surprised they read your facial expressions. They’re just so observant.”

Dr. Greg Nelson, director of surgery and diagnostic imaging at Central Veterinary Associates in Valley Stream, N.Y., said dog owners can use the study findings to be more aware of how they interact with their dogs.

“You should be mindful of your facial expressions,” Nelson said. “You can’t say one thing or use punishment or reward in one way and have your facial cues contradict that.”

Dodman added: “Perhaps a message would be to smile more. You can’t fool a dog.”

The study is published Feb. 12 in the journal Current Biology.

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SOURCES: Ludwig Huber, Ph.D., head, comparative cognition, Messerli Research Institute, University of Veterinary Medicine, Vienna, Austria; Nicholas Dodman, B.V.M.S., professor, animal behavior, Tufts University Cummings School of Veterinary Medicine, North Grafton, Mass.; Greg Nelson, D.V.M., director, surgery and diagnostic imaging, Central Veterinary Associates, Valley Stream, N.Y.; Feb. 12, 2015, Current Biology