Most dog owners can sense the difference between Fido's yip of joy and howl of discontent. Now, scientists find people use the same general rules to recognize doggy emotions as they do for fellow humans.
By comparing how people perceive human and dog vocalizations, researchers found that people linked positive or negative emotions with the length of a vocalization, and the emotional intensity with a sound's pitch.
Emotions reflect a person's mental state, and the evolutionary roots of emotions go way back. Emotional vocalizations are quite similar across different species, and may carry the same information about an animal's inner state as about a human's. [Top 10 Things that Make Humans Special]
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"We are curious how dogs communicate their inner state, and in what extent are humans able to understand this," said study team member Tamás Faragó, who studies animal behavior at Eotvos Lorand University in Hungary.
Previous research found that low-pitched, quickly repeated dog barks are perceived by humans as being higher in aggression, whereas slower, high-pitched barks are seen as more positive. However, barking is a result of domestication, so general rules don't apply to it.
Faragó and his colleagues decided to see whether humans interpret the calls of dogs and other humans in similar ways. They recruited volunteers, 33 women and six men with an average age of 31, and gave them an online survey that included hearing sounds from humans and dogs, such as a baby's laugh or a puppy's whine. The participants had to rate each call on a scale from negative to positive emotion, and from low to high emotional intensity.
The shorter calls, or sounds, were rated as more positive than longer calls, and higher-pitched calls were rated as more intense than lower-pitched ones. The findings, detailed online Jan. 8 in the journal Biology Letters, suggest that humans do indeed use similar characteristics to sense emotion in dogs as they do in other humans.
The ability to tell emotional state from vocalizations likely isn't unique to humans, Faragó told LiveScience. "It seems to be more likely for me that expressing and perceiving emotional states of others is an ancient system rooted deep in our evolution, and we share this ability with several other species," he said.
To prove this, scientists would need to analyze sounds from other species, and test them not just in humans, but also in related species.
Another possibility is that humans judge the emotions of other animals based on their similarity to human sounds. "Recognition of the inner state of others is essential for both empathy and sympathy with other humans or nonhuman animals," Faragó said.
Understanding the rules that help humans interpret others' emotional state could eventually be used to engineer robots that interact with humans, such as service robots for the elderly, Faragó said.