Welcome to our Peculiar Pet Facts series, where we investigate the oddities of our pets and explore the science behind them.
Does your dog wag their tail when you’re laughing? Do they put their head on your lap when you’re upset? Do they start looking sheepish and slinking away when you sternly ask, “Did you spread trash all over the kitchen?” If you answered yes to these questions, you’re familiar with the idea that your dog knows how you’re feeling or what emotions you’re experiencing.
So how does your dog know that you’re happy, sad or angry? Research investigating the ability of dogs to process human emotions as positive or negative may help provide the answer. Here, we summarize two studies that suggest that dogs use your facial expressions and vocalizations (sounds) or just your vocalizations to know (for some emotions) whether you’re experiencing positive or negative feelings. But first, a quick lesson on human emotions and how scientists study them.
Intro to Human Emotions
Psychologists typically 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 connected with each other.
When researchers study emotions, they sometimes use two axes, or dimensions, to apply a value to a stimulus (i.e., how does that “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 as expressed on a continuum from pleasant to unpleasant or from attractive to aversive.” So happiness would typically be a pleasant valance with relatively high arousal and sadness would be an unpleasant valence with relatively low arousal. Another way to look at it is that happiness has a positive valence and sadness has a negative valence.
Dogs Can Match a Happy Face with a Happy Sound
Researchers wanted to learn if dogs can recognize human and dog emotions from what they see and hear. The researchers expected that if dogs could do this, the dogs would look longer at facial expressions that matched the emotional valence of sounds played at the same time (i.e., if they were shown a happy/playful face and an angry/aggressive face and a happy sound was played, they would look at the happy face longer).
To accomplish this, they studied 17 adult dogs of various breeds. They projected a happy/playful face and an angry/aggressive face from 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 a positive or negative valence (spoken/barked by the same individual), or a neutral sound (Brownian noise). One female and one male per species were used. The responses of the dogs (whether they looked longer at the right or left image) were recorded over two sessions with 10 trials per session. The following combinations were assessed: four face pairs (two humans, two dogs) x two vocalizations (positive/negative valence) x two face positions (left, right) plus four control trials (four face pairs with neutral auditory stimulus).
Dogs showed a preference for (looked longer at) the face that matched the valence of the sounds about two-thirds of the time. This preference was observed regardless of whether the test was done with a human or a dog face/sound or if the valence was positive or negative. But dogs did have a stronger response (greater sensitivity) toward dog faces/sounds vs. human faces/sounds. The results suggest that dogs can use what they see and hear to categorize human and dog emotions as positive or negative.
Dogs Can Hear if Emotions Are Positive or Negative
Another study wanted to see if dogs could recognize the six basic human emotions when they were expressed as nonverbal vocalizations (sounds not words) and with no 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).
The results from 30 dogs were analyzed for the study. Men and women were recorded making nonverbal vocalizations for each of the six basic human emotions — laughing (happiness), retching (disgust), screaming (fear), sobbing (sadness), growling (anger) and a strong expiration producing “oh” vocalizations (surprise). Each dog was placed in a room with a food bowl that had speakers equal distance from the food bowl on the left and right (the speakers played the same sound).
The researchers found that dogs turned their head to the right when a happiness sound was played and to the left when fear and sadness sounds were played. There was a trend for dogs to turn their heads to the left with anger sounds but this was not statistically significant. There were no head-turning biases found for disgust or surprise.
The researchers reported that dogs turning their head to the left for fear and sadness vocalizations suggested activation of the right hemisphere of their brains, which is consistent with previous research that the right hemisphere has a dominant role in analysis of intense emotional stimuli and negative emotional valence. Dogs turning their head to the right (left hemisphere activation) after hearing the happiness vocalization suggested that they perceive laughter as a positive emotional state. The happiness vocalization also induced low arousal levels compared to hearing fear and anger vocalizations but not sadness.
The researchers proposed that the reason there was no head-turning bias for disgust and surprise is because these emotions are less distinguishable for dogs and more ambiguous. What disgusts a dog is probably different to what disgusts a human (e.g., whether poop is disgusting or not differs between humans and dogs). And surprise could 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 tuned into how you’re feeling, now you know how they’re doing it. Research like these studies may also help humans better understand how dogs are feeling.
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