Dog lovers may find it obvious that dogs pick up on our emotions. Attending to our emotional expression—in our faces, behavior, or even smell—would help them live intimately by our side.

"Dogs get us," we say. End of story. But what about their side of the story? If dogs attend to our emotions—particularly those we wear on our faces—how might dogs feel when they see our different emotions?

An answer to this question arose almost by accident. In 2015, Corsin Müller and colleagues at the University of Veterinary Medicine, Vienna published a study that sought to determine whether dogs can discriminate happy and angry expression in human faces, as opposed to relying on other cues (their finding: yes, dogs can get this information from our faces alone).

But because of the study design, the researchers could also peer into how dogs might feel about our emotions. In the study, pet dogs saw images of happy or angry human faces on a computer screen. To get a treat, the dogs had to approach and nose-touch a particular image on the screen. These are dogs. They can do this. Nose-touch for a treat? Yes please. A fabulous dog named Michel will now demonstrate:

But when viewing the angry faces, the researchers noticed something odd. Dog performance was affected by whether they saw happy or angry expressions. During the initial training, dogs seeing the angry expression took longer to learn to approach and nose-touch the image for a treat than dogs who saw the happy expression. In other words, dogs were less inclined to approach and nose-touch angry faces, even though doing so would yield a treat.

"Why would I approach an angry person? That makes no sense," a dog might think. Through past experiences with people, dogs could come to view the angry expression as aversive. The researchers suggest that dogs "had to overcome their natural tendency to move away from aversive (or threatening) stimuli…"

Reluctance to approach is but one way to assess how dogs perceive our emotions. To tackle the same question, a new study published in Behavioural Processes turned to a subtle and often overlooked behavior that you might spot more often after today.

Natalia Albuquerque and colleagues from the University of Lincoln and the University of São Paulo presented dogs with images of angry and happy faces. The researchers found that when dogs looked at images of angry human faces, they were more likely to mouth-lick than when they saw happy human faces. And we're not talking about "yum food" mouth-licking.

Mouth-licking, the researchers explain, "is believed to be an indicator of short-term (or acute) stress responses." Mouth-licking has been identified in stressful contexts like if a dog is startled by a loud noise or when a dog is alone and experiencing separation-related issues. In social situations, a quick in / out of the tongue may suggest emotional conflict and could be accompanied by other subtle behaviors that indicate, "Uhm… interact? No, I'd rather keep my distance, thanks." Licking is also commonly found in appeasement or pacifying contexts.

Unlike trembling, whining, excessive barking, and panting—which owners more regularly identify as stress-related—people are less likely to identify subtle behaviors like looking away, turning the head, yawning, and lip-licking as possible indicators of dog discomfort.

Now it should make more sense why the researchers looked at dog mouth-licking: "As the mouth-licking behaviour was associated with the viewing of negative faces," explain the researchers, "it is likely that these negative emotional visual stimuli were perceived as aversive by the dogs."

A dog's extended tongue should be on dog lovers' radar. To clarify, we're not talking about just any tongue extension, like those associated with food, or a happy dog's lolling tongue, or a tongue engaged in licking someone. Although inconsistently labeled and described in the literature, the tongue extension we're discussing today is generally described as an in / out of the tongue that may (or may not) go over the nose. Out in the real world, dogs may display this type of tongue extension in concert with behaviors like lifting a paw, yawning, turning the head / looking away, being still, moving away, or making the body smaller. Seems like we're going to need a bigger radar.

"If a dog starts tongue flicking and turning his head when I reach to pet him, I'm going to pay a lot of attention to it, and probably change my own behavior," offers Patricia McConnell, PhD, CAAB.

So yes, dogs attend to our emotional expression. That's our part of the story. Their part of the story is written in their behavior.

References

Albuquerque N, Guo K, Wilkinson A, Resende B, Mills DS. 2018. Mouth-licking by dogs as a response to emotional stimuli. Behavioural Processes, 146, 42—45.

Müller CA, Schmitt K, Barber ALA, Huber L. 2015. Dogs can discriminate emotional expressions of human faces. Current Biology, 25, 601—605.