Acoustics of laughter: New insights into this mysterious form of expression

While scientists have thoroughly researched many other human sounds, such as singing and talking, remarkably little is known about the acoustics of laughter. Seeking to rectify this, Vanderbilt psychologist Jo-Anne Bachorowski and Cornell psychologist Michael Owren studied 1024 laughter episodes from 97 young adults as they watched funny video clips from films such as "When Harry Met Sally" and "Monty Python and the Holy Grail." The surprising results were published in the September 2001 issue of the Journal of the Acoustical Society of America.

"We tend to think of laughter as being tee-hee or ho-ho, sorts of sounds," said Bachorowski. But their results showed otherwise.

First of all, laughers produce many different kinds of sounds, including grunts and snorts. The investigators found interesting sex differences in the use of these sounds, with males tending to grunt and snort more often than females.

The sex differences don't end there. Women produced more song-like laughter than men. These song-like laughs are "voiced," meaning that they involve the vocal folds, the tissues in the larynx involved in producing vowels and related sounds.

In men and women alike, laughs are surprisingly high-pitched. To determine this, the researchers took each voiced laugh and measured its "fundamental frequency," which corresponds to the rate at which the vocal folds vibrate, and is heard by listeners as pitch. They found that women's laughter, on the average, was twice as high-pitched as normal speech (had twice the fundamental frequency). Men's laughter was, on the average, 2.5 times more higher-pitched than their normal speech (had 2.5 times the fundamental frequency).

Even more remarkable were the very high frequencies of some voiced laughs. Male fundamentals were sometimes over 1,000 Hertz (Hz)-about the pitch of a high "C" for a soprano singer. Females were sometimes over 2,000 Hz-one octave higher than a soprano's high C. These high fundamentals were unexpected. "I personally didn't imagine that males and females would produce sounds with fundamentals that high in natural circumstances," Bachorowski said.

Santa Claus may also have to change his tagline, as researchers found that voiced laughter does not consist of articulated vowel-like utterances, like "tee-hee," "ha-ha," or "ho-ho." Instead, laughter is predominantly composed of neutral, "huh-huh" sounds.

Ever think your laugh sounds funny when you're stressed out? The researchers found lots of evidence that laughter can be associated with out-of-the-ordinary vocal physics, such as whirlpools of air or whistles near the larynx. While the researchers don't know with certainty what the origins of such effects are, they may be associated with a high level of emotional arousal on the part of laughers.

The researchers are in the midst of further studies of laughter. For example, they are studying the impact that these sounds have on emotional responses in listeners. They are also looking to uncover what happens in the human brain when listeners hear laughter. Another piece of their work involves studying whether laughter is speech-like in the sense of providing "meaning" or symbolic value to listeners. The investigators instead think that laughter functions largely to sway a listener's emotional response, with any meaning attributed to the sounds inferred or interpreted from the situation in which the laughter is produced.

This research was funded by the National Science Foundation.