Welcome to our Peculiar Pet Facts series, where we investigate the quirks of our pets and explore the science behind them.
Does your dog wag its tail when you laugh? Do they put their head in your lap when you’re upset? Do they start to look sheepish and walk away when you sternly ask, “Did you scatter trash all over the kitchen?” If you answered yes to these questions, you know the idea that your dog knows what you are feeling or what emotions you are feeling.
So how does your dog know when you’re happy, sad, or angry? Research looking at dogs’ ability to process human emotions as positive or negative might help provide the answer. Here, we summarize two studies that suggest dogs use your facial expressions and vocalizations (sounds) or just your vocalizations to tell (for some emotions) whether you’re experiencing positive or negative feelings. But first, a quick lesson on human emotions and how scientists study them.
Introduction to human emotions
Psychologists generally classify human emotions into six categories – happiness, sadness, anger, surprise, fear and disgust – although some research suggests that there may be at least 27 distinct emotions that are intimately linked to each other.
When researchers study emotions, they sometimes use two axes, or dimensions, to apply value to a stimulus (i.e., how does this “thing” make you feel?). According to the American Psychological Association, the two axes are arousal (assigned as a value between high and low) and emotional valence. Emotional valence is “the value associated with a stimulus expressed on a continuum from pleasant to unpleasant or attractive to aversive”. Thus, happiness would generally be a pleasant valence with relatively high arousal and sadness would be an unpleasant valence with relatively low arousal. Another way of looking at it is that happiness has a positive valence and sadness has a negative valence.
Dogs can associate a happy face with a happy sound
The researchers wanted to know if dogs could recognize human and canine emotions from what they see and hear. The researchers expected that if the dogs could do this, the dogs would look longer at facial expressions that matched the emotional valence of the sounds being played at the same time (that is, if they were shown a face happy/playful and an angry/aggressive face and a happy sound was played, they looked at the happy face longer).
To do this, they studied 17 adult dogs of different breeds. They projected a happy/playful face and an angry/aggressive face of a human or a dog onto two screens (placed in front of them) at the same time that a single vocalization was played. The vocalizations were a dog bark or a human voice in an unfamiliar language with either positive or negative valence (spoken/barked by the same individual) or neutral sound (Brownian noise). One female and one male per species were used. The dogs’ responses (whether they look longer at the right or left image) were recorded over two sessions with 10 trials per session. The following combinations were evaluated: four pairs of faces (two humans, two dogs) x two vocalizations (positive/negative valence) x two face positions (left, right) plus four control trials (four pairs of faces with auditory stimulus neutral).
The dogs showed a preference for (looked longer) the face that matched the valence of sounds about two-thirds of the time. This preference was observed regardless of whether the test was performed with a human or a dog face/sound or whether the valence was positive or negative. But the dogs had a stronger response (greater sensitivity) to dog faces/sounds compared to human faces/sounds. The results suggest that dogs can use what they see and hear to categorize human and canine emotions as positive or negative.
Dogs can hear whether emotions are positive or negative
Another study wanted to see if dogs could recognize the six basic human emotions when expressed as nonverbal vocalizations (sounds, not words) and without visual context (no faces to look at). They assessed the arousal dimension by recording the dogs’ behaviors and cardiac activities and the emotional valence dimension by recording which way the dogs turned their heads (left or right).
Results from 30 dogs were analyzed for the study. Men and women have been recorded making non-verbal vocalizations for each of the six basic human emotions – laughing (happiness), vomiting (disgust), screaming (fear), sobbing (sadness), growling (anger) and a strong exhalation producing “oh” vocalizations. (surprise). Each dog was placed in a room with a food bowl that had speakers equidistant from the food bowl on the left and right (the speakers played the same sound).
The researchers found that the dogs turned their heads to the right when a sound of happiness was played and to the left when sounds of fear and sadness were played. There was a tendency for the dogs to turn their heads to the left with angry sounds, but this was not statistically significant. There were no staggering prejudices found for disgust or surprise.
Researchers reported that dogs turning their heads to the left for vocalizations of fear and sadness suggested activation of the right hemisphere of their brain, which is consistent with previous research that the right hemisphere has a dominant role in the analysis of intense emotional stimuli and negative emotional valence. . Dogs turning their heads to the right (left hemisphere activation) after hearing the happiness vocalization suggest that they perceive laughter as a positive emotional state. Happiness vocalization also induced low levels of arousal compared to fear and anger vocalizations, but not sadness.
The researchers proposed that the reason there was no disgust and surprise bias is because these emotions are less distinguishable for dogs and more ambiguous. What disgusts a dog is probably different from what disgusts a human (for example, whether or not poo is disgusting differs between humans and dogs). And surprise can be a positive or negative emotion depending on the circumstances.
The results of this study show that dogs can process some basic human nonverbal emotional vocalizations as positive or negative – without seeing the human’s face.
So the next time your dog seems to be tuned in to how you feel, now you’ll know how he’s doing. Research like these studies can also help humans better understand how dogs feel.
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