How Do Dogs Respond to Human Emotional Vocalizations?

March 23, 2018
JoAnna Pendergrass, DVM

Dr. Pendergrass received her DVM degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory Universitys Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner ofJPen Communications, a medical communications company.

A recent study provided new insight into how dogs process and respond to nonverbal vocalizations of human emotion.

Over thousands of years of domestication, dogs have gained many social and cognitive skills for communicating with humans. For example, dogs can recognize emotions conveyed by human facial expressions and differentiate between positive and negative human emotional sounds.

Interestingly, dogs demonstrate lateralized behavior in response to human vocalizations. This behavior, which reflects brain asymmetries, helps characterize head-turning behavior following acoustic stimuli. In vertebrate animals, right head turns (left brain dominance) reportedly indicate the processing of negative emotions and left head turns (right brain dominance) signify the processing of positive emotions.

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However, “it remains unclear how dogs perceive and process the 6 basic emotions expressed by human nonverbal communications,” wrote the authors of a recent Nature Scientific Reports publication.

Measuring Responses

To fill this knowledge gap, the authors evaluated how dogs respond to nonverbal human emotional sounds. First, 14 men and women recorded vocalizations of the 6 basic human emotions: happiness, surprise, disgust, fear, sadness, and anger. These recordings were then divided into 3 sets of 6 vocalizations, with each vocalization representing 1 emotion.

For testing, each of the 30 dogs in the study listened to 1 of these 3 sets. The testing room contained 2 speakers and a food bowl centrally positioned between the speakers. After a dog’s owner led their dog to the food bowl, vocalizations were played in a random order. Using video recording, the authors analyzed head-turning behavior and other behavioral responses.

During testing, dogs wore a wireless cardiac monitoring device. Before testing, each dog owner completed a questionnaire on their dogs’ reactivity in certain situations, such as stranger-directed aggression.

Results

Head turns

The percentage of head-orienting responses was similar across vocalizations (77% — 93%). Fear, sadness, and anger vocalizations elicited left head turns, indicating right brain dominance in response to negative emotional sounds. In contrast, the happiness vocalization provoked right head turns, indicating left brain dominance after hearing positive emotional sounds. Tail wagging, also indicative of left brain activation, was observed with the happiness vocalization, suggesting the dogs’ positive perception of this vocalization.

Surprise and disgust vocalizations did not elicit head turn bias, possibly because their emotional valence is ambiguous to dogs.

Reactivity time (between hearing the vocalization and stopping feeding)

The probability to react was variable. For example, dogs were more likely to react after hearing the happiness vocalization if they demonstrated stress-related behaviors during testing. Reactivity was less likely in older dogs as well as for vocalizations played after the sadness vocalization.

Latency time (time to resume feeding)

Likelihood to resume feeding decreased due to several factors, including increasing age, stress-related behavior during testing, and hearing the anger vocalization.

Cardiac activity and behaviors

Heart rates were variable. For example, compared to baseline, heart rates increased more after hearing the anger vocalization than other vocalizations. Regarding behaviors, stress-related behaviors were more likely after hearing the anger vocalization. Also, dogs who had strong stranger-directed aggression and non-social fear, as reported by their owners, were more likely to demonstrate stress-related behaviors during testing.

Bringing it Together

The authors concluded that the study’s findings “provide evidence about the existence of an emotional modulation of the dog brain to process basic human nonverbal emotional vocalizations.” In addition, the cardiac activity and behavior responses indicate that dogs are sensitive to human emotional sounds. Investigating head-turn behavior along with other behavioral and physiological responses, the authors believe, is a useful tool to more deeply understand how animal process emotions.

Dr. Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.