When you look into your dog’s eyes, you probably try to guess what he’s thinking. You might read that puppy dog look as begging or see a loving gaze as affection. Just as we try to read other people’s expressions, we attempt to learn what our dog is feeling based on the way he looks at us. Now scientists are getting in on the action and using dogs’ eyes to gain insight into how they’re feeling.
Researchers at the University of Helsinki looked at the effect of the hormone oxytocin on the gazing behavior of domestic dogs in an emotion-perception task. Oxytocin plays a key role in the relationship between people and dogs and is associated with love and trust. In fact, simply looking into your dog’s eyes can release the hormone in both you and your pet. This study allowed experimenters to see how boosting the dogs’ oxytocin levels affected their gaze behavior.
During the emotion-perception task, the dogs looked at photographs of unfamiliar male human faces on a computer screen. In one-half of the photos, the men had happy expressions and in the other half they had angry expressions, so the dogs were distinguishing the emotional state of the person they were looking at and reacting accordingly.
Forty-three dogs participated in the study, including 16 different breeds, as well as mixed-breed dogs. Each dog participated twice in the task, once with boosted oxytocin levels (administered with a nasal spray), and once without (a placebo consisting of a saline solution nasal spray). To determine the effect of the oxytocin, the researchers couldn’t ask the dogs how they felt or what they were looking at. However, they could observe the dog’s pupil size and the path of his gaze, both of which are regulated by emotions.
Using an eye-tracking device, which measured pupil size and exactly where the dogs were looking in each situation, the scientists were able to use the dog’s eyes to measure their attention and emotional arousal. The system was painless and unobtrusive. The dogs were trained to hold their chin on part of the device, while they looked at a monitor, and the infrared eye tracker did the rest.
The results showed that without the oxytocin boost, the dogs had the largest pupils when looking at the angry faces. The larger the pupil, the greater the attention and emotional arousal. This makes sense, as the angry face would be considered more threatening. Once the dogs had been given the oxytocin boost, things reversed. The happy faces caused the largest pupil sizes. In other words, it looks like the oxytocin made the smiling faces more appealing and the angry faces less intimidating.
In addition, gaze behavior changed, depending on the situation. After the oxytocin boost, the dogs spent less time fixated on the eyes of the angry faces and instead showed more fixations toward the eye region of happy faces. The dogs also revisited or glanced back at the eyes of the happy faces more often after the oxytocin boost and more often than the eyes of the angry faces.
Overall, it seems that boosting the dogs’ oxytocin levels changed what they chose to pay attention to and what caused the greatest emotional arousal. The hormone influenced the dogs’ attention away from possible threat and toward smiling faces, which supports what is known about oxytocin and how it relieves social anxiety and promotes positive social behavior. This provides further support for the role oxytocin plays in the unique social skills dogs exhibit toward humans.
An exciting revelation from the study involves the researchers’ methods. Although eye-tracking devices have been used in human research, and pupil measurements have been used as a window into the emotions of people and apes, this study was one of the first to apply the technology to dogs.
The researchers caution that eye movements and pupil data alone are not enough to draw firm conclusions about a dog’s emotional state, but considering that we can’t ask dogs how they feel, it’s a great start. If eye movements and pupil size truly make a dog’s eyes the windows to their soul, what else could similar experiments tell us about the thoughts and feelings of our closest companions?