Recognizing the emotional expressions of others is a critically important social skill that is seen in many types of animals. The ability to understand emotions can also occur outside of a single species when social partners are not all contained within one species. This cross-species understanding and communication has been best studied within the biological miracle of the friendship between humans and dogs.
There has been strong evolutionary pressure for dogs to understand human expressions, motivation and behavior, and this has led to their ability to read people’s emotions. Researchers have demonstrated that dogs can tell neutral human expressions from emotional ones and can also discriminate angry human faces from happy ones. Dogs are capable of facial recognition with humans, and process the visual input from human faces much as people themselves do. Dogs have a specialized part of their brain within the cortex that is used when processing information about human faces, which at least partially explains how good they are at tasks related to identifying our faces and understanding our emotional expressions. Despite the large amount of previous research, there is still much to learn about the subject.
Humans tend to have a bias towards the right side of the brain when it comes to both expressing and processing emotional expressions, but the research about dogs has shown mixed results in this area. To understand the results of any research about sides of the brain (lateralization), it is critical to know that with a few exceptions, each side of the brain controls the opposite side of the body, so a right-brain bias is expressed as a bias of the left side of the body.) Dogs tend to use the right side of their brain more when viewing human faces, as revealed by their tendency to look towards the left when viewing human faces with neutral expressions. However, it is not clear if they have a side bias when observing human faces with emotional expressions.
A new study expands on the way that dogs read and process humans emotional expressions, exploring the ways different sides of the brain process emotion. By studying the lateralization of dogs’ responses to emotions as well as their physiological responses, researchers are expanding our knowledge of how canines react to human emotional expressions. These investigations expand our understanding of how canine brains process the information they receive from human faces.
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The specific questions in Orienting asymmetries and physiological asymmetries in dogs’ response to human emotional faces concern whether the dogs have a lateralized response to different emotional expressions of humans. Researchers also explored their physiological and behavioral responses to seeing those expressions.
Dogs in the study were exposed to neutral human faces as well as faces showing the six basic cross-culturally recognized emotions: fear, anger, sadness, disgust, surprise, happiness. (These are often called Ekman’s six universal emotions after the scientist who studied them so intensely.) While eating, dogs were positioned between two screens that simultaneously displayed the same picture of a human face displaying an emotion or a neutral expression. One screen was 1.9 meters away to the dog’s left and the other was the same distance away but to the dog’s left.
Researchers recorded whether the dog turned to the left, turned to the right, or did not orient in either direction within 6 seconds, as well as how long it took for the dog to look one way or another. The time it took for the dog to return to eating was noted, though if the dog failed to resume eating within 5 minutes, the experimental session was ended. From videotapes of the experiment, researchers collected data on whether the dogs displayed any of 26 behavior patterns such as tail tucking, lip licking, freezing, whining, running away and yawning, all of which could indicate stress. The cardiac activity of dogs was also recorded.
The results of the study found that dogs were more likely to turn to the left (indicating a bias for using the right side of the brain) when the emotional expressions were those of fear, anger and happiness. Conversely, dogs were more likely to turn to the right (left side of the brain bias) in response to the expression of surprise. Dogs did not show a statistically significant side bias in response to neutral expressions or to the emotions of sadness and disgust. The cardiac data show elevated heart rates that lasted longer in response to the emotions that caused a look to the left: fear, anger and happiness. This suggests that highly arousing emotions are processed in the right side of the brain. In previous studies of expressions, dogs orient left in response to negative emotions, but turn right in response to positive ones. If this pattern had held, the dogs would not have turned left in response to happy expressions. The authors of the paper suggest that baring the teeth in a smile may be confusing to dogs when such an image is viewed by a dog’s peripheral vision, and they may perceive it as threatening in some way.
Another result of the study is that dogs took longer to go back to eating after seeing an angry face than after seeing any of the other expressions. They showed more stress-related behaviors after viewing faces that were angry or happy than any of the other images.
Brian lateralization and canine perception of human emotional expressions are active areas of research and we can expect new studies to appear soon.