The spontaneous sounds that we make to express everything from elation to embarrassment, such as 'woohoo' and 'oops', convey at least 24 kinds of emotion, according to a study on people from four countries, including India.
Scientists at the University of California (UC), Berkeley in the US conducted a statistical analysis of listener responses to more than 2,000 nonverbal exclamations known as "vocal bursts" and found they convey a lot more about what we are feeling than previously thought.
Previous studies of vocal bursts set the number of recognisable emotions closer to 13.
The results, published in the American Psychologist journal, are demonstrated in vivid sound and colour on the first-ever interactive audio map of nonverbal vocal communication developed by researchers.
"This study is the most extensive demonstration of our rich emotional vocal repertoire, involving brief signals of upwards of two dozen emotions as intriguing as awe, adoration, interest, sympathy and embarrassment," said Dacher Keltner, a professor at UC Berkeley.
For millions of years, humans have used wordless vocalisations to communicate feelings that can be decoded in a matter of seconds, researchers said.
"Our findings show that the voice is a much more powerful tool for expressing emotion than previously assumed," said Alan Cowen, a PhD student at UC Berkeley.
In the audio map, a user can slide one's cursor across the emotional topography and hover over fear (scream), then surprise (gasp), then awe (woah), realisation (ohhh), interest (ah?) and finally confusion (huh?).
Among other applications, the map can be used to help teach voice-controlled digital assistants and other robotic devices to better recognise human emotions based on the sounds we make, he said.
Though limited to US responses, the study suggests humans are so keenly attuned to nonverbal signals -- such as the bonding "coos" between parents and infants -- that we can pick up on the subtle differences between surprise and alarm, or an amused laugh versus an embarrassed laugh.
Researchers recorded more than 2,000 vocal bursts from 56 male and female professional actors and non-actors from the US, India, Kenya and Singapore by asking them to respond to emotionally evocative scenarios.
More than 1,000 adults recruited via Amazon's Mechanical Turk online marketplace listened to the vocal bursts and evaluated them based on the emotions and meaning they conveyed and whether the tone was positive or negative, among several other characteristics.
A statistical analysis of their responses found that the vocal bursts fit into at least two dozen distinct categories including amusement, anger, awe, confusion, contempt, contentment, desire, disappointment and disgust.
For the second part of the study, researchers sampled YouTube video clips that would evoke the 24 emotions established in the first part of the study, such as babies falling, puppies being hugged and spellbinding magic tricks.
This time, 88 adults of all ages judged the vocal bursts extracted from YouTube videos, researchers said.
Again, the researchers were able to categorise their responses into 24 shades of emotion.
"These results show that emotional expressions colour our social interactions with spirited declarations of our inner feelings that are difficult to fake, and that our friends, co-workers, and loved ones rely on to decipher our true commitments," Cowen said.
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