It's not just your imagination: Your dog really can tell when you're having a rough time. In fact, a new study found that dogs can actually read their owners' faces and understand several different human emotions.
The new research was published in the journal Learning & Behavior in June, and found that the dogs behaved differently when shown pictures of emotional human faces.
For the study, scientists showed a group of 26 dogs photos of a human face displaying one of the six basic human emotions: anger, fear, happiness, sadness, surprise and disgust. Another face just showed a neutral expression. The models were asked to make the face with "with the greatest intensity as possible," according to the study.
When dogs were shown facial expressions like anger, fear and happiness, their heart rates rose and they took longer to begin eating again than if they were shown a more neutral face. They also tended to turn their heads to the left.
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The scientists said this indicated the dogs were experiencing more stress, and the reason the dog may be stressed by a happy face could be because instinct makes dogs uneasy when they see bared teeth, the scientists speculated in the study.
When they were shown a face of surprise, the dogs turned their heads to the right, which could be because they see surprise as a non-threatening expression, the scientists wrote in a news release. There was little behavioral change when the dogs were shown disgusted or sad faces.
The study backs up some research from 2016 that showed dogs were able to process and understand human emotion. Previously, it was thought dogs may only be repeating learned behavior without understanding it.
In that study, scientists played a recording of a voice and displayed photos of facial expressions to 17 different dogs. The dogs spent more time looking at facial expressions that matched the tone of the voice on the recording. "Our findings are the first to show that dogs truly recognize emotions in humans and other dogs," study co-author Daniel Mills wrote in a news release a the time.
Dogs, which have been bred as human companions for thousands of years, may even be born with the ability to connect with people — something that does not seem to happen with dogs' close ancestor, the wolf.
"Wolves, even when raised in a human environment, are not as flexible with human communication as dogs," cognitive psychologist Juliane Kaminski told Discovery News in 2012. "Dogs can read human gestures from very early ages on."
For the new study, the scientists say the dogs turning their heads in a certain way also points to evidence that emotions are processed in different areas of the canine brain.
"Clearly arousing, negative emotions seem to be processed by the right hemisphere of a dog's brain, and more positive emotions by the left side," said study author Marcello Siniscalchi in a news release.