And they’re letting you know they know. Just look at those puppy dog eyes.

Scientists at the University of Portsmouth’s Dog Cognition Center have found clear evidence that dogs change their expressions in direct response to human attention, according to a new study published in the journal Scientific Reports.

Previous studies have suggested that the facial expressions of nonhuman primates like orangutans and gibbons vary more when people are around, especially during play, indicating that those expressions are not necessarily an automatic response but a direct response to having an audience.

But the Portsmouth study is the first to find a link between dogs’ facial expressions and the presence of people.

The study’s lead researcher, Dr. Juliane Kaminski, said, “The findings appear to support evidence that dogs are sensitive to humans’ attention and that expressions are potentially active attempts to communicate, not simple emotional displays.”

Kaminski’s team studied 24 dogs of differing breeds. All were family pets who were used to being around people. Specifically, the researchers tested how the dogs’ facial expressions changed in response to a highly arousing but nonsocial stimulus (food) compared to how they changed in response to the attention of a human.

Researchers filmed the dogs’ faces during a variety of exchanges with a human, from the human facing the dog and making eye contact while holding food, to facing the dog and making eye contact without food, and facing away from the dog.

The team measured the dogs’ facial expressions using technology known as DogFACS (the Dog Facial Action Coding System), a scientific observational tool for identifying and coding facial movements in dogs based on underlying muscle movements.

They discovered that the dogs produced more facial expressions when the humans were facing them than when they turned away, with or without holding food.

Eye contact was the key.

Kaminski wasn’t surprised. She said, “We knew domestic dogs paid attention to how attentive a human is.” She said a previous study had shown that dogs stole food more often when the human's eyes were closed or they had their back turned. Another study showed that dogs follow the gaze of a human if the human first establishes eye contact with the dog. “So the dog knows the gaze-shift is directed at them.”

Kaminski added, "This study moves forward what we understand about dog cognition. We now know dogs make more facial expressions when the human is paying attention."

Which means that when a dog makes a face at you, she may be trying to communicate.

The most common expression produced by the dogs during the study was brow raising. Brow raising makes the eyes look bigger, producing the effect of so-called puppy dog eyes.

In humans, puppy dog eyes can resemble sadness. In dogs, it can make their eyes appear larger and more baby-like. That could tap into human’s preference for child-like characteristics, making us especially responsive to that expression in dogs.

After all, people make puppy dog eyes at you when they want something. So it’s no surprise that puppies do it, too.

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