HaHaHa! The Acoustics of Laughter:

HaHaHa!

The Acoustics of Laughter:
New Insights into this Mysterious Form of Expression

Humans have many ways to express themselves, but one of the most enjoyable - and mysterious - is laughter. More than a frivolous emotional outburst, laughter has many important functions in human communication, playing major roles in social situations ranging from dates to diplomatic negotiations.

Web Resource: Laughter's Influence Vanderbilt University

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 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 comprised 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.

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The researchers discovered that people produce a wide variety of laugh sounds with a remarkable range of vocal pitch. In particular, they determined that individuals vary both the number and kinds of laughs they produce depending on the sex of their social partner and whether their social partner is a friend or stranger.

"We think that laughter is one of a package of subtle yet effective tools, like physical proximity and eye gaze, that people use, albeit unconsciously, to shape the emotional and behavioral responses of others," Bachorowski said.

They found that individual women, for example, produced laughs with markedly high and variable pitch when in the company of male strangers.

Other findings of the study include:

· Men's laughter is linked to the history of their relationship with their social partner. When paired with friends of either sex, men laughed significantly more than men who were tested alone or with a male or female stranger.

· Women's laughter is linked to the sex of their social partner. Females paired with a male friend produced more laughs than females tested alone, with a female friend, or with a male stranger.

· When paired with male strangers, women's laughter tends to be higher pitched, indicative of smaller body size, possibly exploiting men's propensity to be attracted to females with juvenile features.

· People have a rich repertoire of laugh sounds, with some sounding more like bird chirps, pig snorts, frog croaks and chimpanzee pants than normal human utterances.

· Laughs can be separated into three basic categories: (1) High-pitched, song-like laughs, which fit our stereotyped notions of laughter; (2) Snort-like laughs, with sounds produced primarily through the nose; and (3) Grunt-like laughs produced through the mouth.

In a second study, which is in press in the journal Psychological Science, Bachorowski and Owren asked other listeners to rate examples of the different laugh types in terms of their friendliness, sexiness, how interested they would be in meeting the laugher, whether they thought the laugh should be included in a laugh track, and the extent to which it elicited a positive emotional response.

Regardless of the rating scheme, the researchers found that listeners were more likely to rate comparatively stereotypical, song-like laughs more positively than the other types.

"These results support the notion that one important function of laugh acoustics is to influence the emotional responses of listeners," Bachorowski said.

From an evolutionary perspective Owren and Bachorowski speculate that human laughter evolved as a way to form alliances. First came the smile, which communicated a positive disposition to other individuals. Over time, however, smiles became increasingly easy to fake, so a more complex signal was needed. That is where laughter came in. Because laughter uses more neural systems and has greater energy costs, it is more difficult to fake. So, at some point, laughter supplanted smiling as an honest signal of an interest in joining forces.