If you've ever amused yourself by making different faces at your dog to see how they'd react, you're not alone. Most dog owners are quick to confirm that their canine friends are adept at understanding human emotions, and there is no shortage of adorable videos out there showing dogs' reactions to excited or sad faces. Do dogs actually understand human facial expressions, though?
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All domestic dogs are descended from an extinct wolf ancestor, and domestication by humans began between 20,000 and 40,000 years ago. The wide array of modern dog breeds is largely due to artificial selection, in which certain physical or behavioral traits are intentionally selected for and amplified over generations. The dog and human bond that so many of us enjoy goes back thousands of years, and over that time dogs have become incredibly in sync with their human companions. Whether they're running agility courses, sniffing for bombs, or helping a person with a disability navigate the world, dogs are able to understand an amazing array of concepts through communicating with their humans — despite a lack of a common language.
Dogs are social creatures who communicate with each other primarily through body language. Most people will instantly recognize a wagging tail as a sign of a happy pup or a tucked tail as indicating fear or stress — but there are many more subtle cues that dogs use to communicate with each other. Dogs' ancestors had a complex social structure that required them to work together, resolve differences, establish boundaries, and show affection — all of which demanded excellent communication. Dogs use their entire bodies to communicate, and while they aren't capable of making near as many facial expressions as humans (over 10,000!), their faces are nevertheless an important factor in relaying information to one another.
A dog’s brain
It's notoriously challenging to study the nuances of dog psychology because, well, we can't just ask them all the questions we have. Researchers most commonly use functional magnetic resonance imaging (which measures changes in blood flow that occur with brain activity) combined with, heart monitors and cameras to measure physical and neurological changes in response to stimuli. Hundreds of studies have been conducted in an attempt to learn whether or not dogs can understand human facial expressions. The answer is one we commonly find in scientific fields — "it depends."
One recent study concluded that there was no difference in dog brain activity when looking at a human face or the back of a human head, suggesting dogs don't differentiate much between the two and therefore are not particularly cued in to faces. This study noted that unlike humans, who have a specific brain region responsible for recognizing and processing faces, there is no analogous structure in dogs.
A different study, however, showed a clear difference in brain activity when dogs were shown images of human faces expressing different emotions. Dogs who viewed happy or neutral faces showed brain activity in the right temporal cortex, while dogs who viewed angry, sad, or fearful faces showed brain activity mainly in the left hemisphere. There was no clear evidence to determine whether dogs could differentiate between individual emotions — one set of brain activity was consistent with the "positive" emotions (happy/neutral) while another set was consistent with "negative" emotions (angry/sad/fearful), but did not show large enough differences to indicate that a dog could necessarily tell the difference between an angry and a sad human face.
Other studies have also found brain activity and physical responses in dogs correlate to viewing certain human facial expressions.
How does my dog know how I'm feeling?
Though dogs' brains may not contain a dedicated face-processing region, this doesn't mean they are incapable of understanding facial expressions. Most human communication occurs through spoken language, but our nonverbal communication is also an important part of how we interact — and dogs are body language experts.
Dogs are intelligent, have exceptional senses of smell and hearing, and are highly attuned to their human companions. When it seems like a dog can understand our emotions, it's likely that they are picking up on a variety of cues using many of their senses to interpret the situation. Studies have shown that dogs respond differently to positive and negative human vocalizations such as laughing, yelling, and crying. Dogs can even detect feelings through their incredible noses by picking up on chemical signals produced by humans during different emotional states.
In studying the brain activity of dogs, it's not absolutely clear whether they can process human facial expressions in the same way that people can. Brain imaging can tell researchers quite a bit, but it's only one part of the puzzle when it comes to dog psychology. Scans can show brain activity, but not necessarily the thoughts or feelings associated with it.
Dogs have evolved alongside humans and have developed a close relationship with us, including understanding our verbal and nonverbal communication. It's quite possible dogs can understand human facial expressions to some degree, but use their other senses to fill in the gaps in order to interpret our feelings.
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