Dogs’ ability to communicate with humans is unlike any other species in the animal kingdom. They can sense our emotions, read our facial expressions, and even follow our pointing gestures. They seem to possess a special skill for knowing exactly how we’re feeling. But not much is known about the role that hearing plays in that ability. Recent research from the Department of Veterinary Medicine at the University of Bari Aldo Moro in southern Italy looked at how dogs process human emotions based only on our vocalizations.
Previous studies have shown that dogs can combine hearing and sight to match happy and angry human faces with happy and angry vocalizations. When using only their hearing, researchers found that dogs can distinguish the positive sound of laughing from the negative sound of crying, and that negative sounds upset and arouse dogs more than positive ones. There are six basic emotions that humans can recognize from vocalizations, regardless of culture: fear, sadness, anger, disgust, surprise, and happiness. The current study aimed to investigate if dogs can recognize all six from nonverbal vocalizations alone.
Thirty dogs were tested in a simple setup. The dogs were given food in a bowl in the center of a testing room, and two speakers were evenly spaced on either side of the bowl. This put the dog an equal distance from each speaker. While the dogs were eating, the speakers played nonverbal human sounds. For example, fear sounds were screams and happy sounds were laughs. The reaction of the dogs to each sound was videotaped.
The scientists were interested in whether the dogs turned their heads to the right speaker or to the left, although both speakers were playing the same sounds. There are two reasons why this is important. The first is because dogs, like humans, use the left side of their brain to control the right side of their body, and vice versa. The second is that previous research has shown dogs tend to process emotionally positive sounds with the left side of their brain and emotionally negative sounds with the right. If the dog turned to the left upon hearing the sound, it would indicate he was processing that sound with the right side of his brain, and therefore, interpreted it as negative.
Results showed that dogs turned to the left for the fear and sadness vocalizations. The trend was the same for anger, but the results were not statistically significant. This indicates the dogs were processing these particular sounds on the right side of their brain, and therefore interpreted them as negative. For happy sounds, the dogs turned to the right, showing that they interpreted them as positive.
Disgust and surprise didn’t show any significant trends, perhaps because those emotions are more context dependent. For example, poop may be disgusting to humans, but it’s exciting to dogs. So, the dogs may not have known how to interpret the disgust and surprise without further information.
Overall, it seems that dogs can determine human emotions using only their ears, at least for happiness, fear, and sadness — using the right side of their brain for processing negative emotions and the left side for positive ones. Additional data collected on heart rate and behavior, such as tail wagging and yawning, supported these findings. That means future studies of head turning, matched with behavior and physiological data such as heart rate, could allow new insight into animal emotions. We can’t ask dogs how they feel in a given situation, but by using these methods, we may be able to determine whether those feelings are positive or negative.