Researchers continue to show just how close the relationship between humans and dogs are. New findings demonstrate how dogs show signs of stress when seeing sad or angry human faces. They may also use different parts of their brain to process our expressions.
The study titled “Orienting asymmetries and physiological reactivity in dogs’ response to human emotional faces” was published in Springer’s journal Learning & Behavior on June 19.
Twenty-six dogs were recruited as participants for the study where they were shown photos of two human adults, one male and one female. They were devoid of makeup, spectacles, piercings, and other accessories that could distract a dog or influence the response. Each photo showed them expressing one of the six basic human emotions: anger, fear, happiness, sadness, surprise, disgust or neutrality.
Each of the dogs was led into a room with a bowl of food at the center. The photos were displayed in a slideshow on either side of the dog, where they remained for 4 seconds each. A video camera recorded the animal’s visual responses during the experiment while a multiparameter wireless system recorded its heart activity.
“Overall, our data showed that dogs displayed a higher behavioral and cardiac activity in response to human face pictures expressing clear arousal emotional states, demonstrating that dogs are sensitive to emotional cues conveyed by human faces,” the authors wrote.
Heart activity of the dogs was found to increase when they were shown pictures of the adults expressing anger, fear, and happiness. This meant the heart rates of dogs may rise when they see someone who is having a bad day, the authors added. The dogs also took longer to resume feeding after seeing these images, experiencing higher levels of stress when looking at such expressions.
While stress is the same response humans would have to angry and fearful expressions, the authors suggested that “dogs process human smiling faces differently” compared to humans. Aspects like bared teeth and lifted lips may trigger a behavioral response in dogs since they did not have auditory information (such as laughter) supplied with the images.
Observed trainers looked at the recorded camera footage and analyzed the visual responses. The head-turning preferences provided evidence that dogs may be using different parts of their brains to process human emotions.
Dogs were likely to turn their heads to the left (i.e. dominant activity in the right side of the brain) when they saw human faces expressing anger, fear or happiness.
However, they tended to turn their head to the right (i.e. dominant activity in the left hemisphere) when seeing surprised facial expressions, possibly since they were viewed as non-threatening.
“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 from the University of Bari Aldo Moro in Italy.