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The study of laughter provides a novel approach to the mechanisms and evolution of vocal production, perception and social behavior

Robert Provine

Laugh Tracks and Contagion

The use of laughter to evoke laughter or a positive mood is familiar to viewers of situation comedy shows on television. "Laugh tracks" (dubbed-in sounds of laughter) have accompanied most "sitcoms" since 7:00 p.m. (Eastern Standard Time) on September 9, 1950. On that evening the Hank McCune Show—a comedy about "a likeable blunderer, a devilish fellow who tries to cut corners only to find himself the sucker"—first used a laugh track to compensate for the absence of a live audience. Despite the fact that the show was short-lived, the television industry discovered the power of laughter to evoke audience laughter. The recording industry recognized the seductive power of laughter shortly after World War I with the distribution of the OKeh Laugh Record, which consisted of trumpet playing that was intermittently interrupted by laughter. It remains one of the most successful novelty records of all time. Acknowledging the commercial potential of this novelty market, Louis Armstrong, Sidney Bechet, Woody Herman and Spike Jones all attempted to cash in with laugh records of their own.

In the intervening years social scientists have confirmed that laugh tracks do indeed increase audience laughter and the audience's rating of the humorousness of the comedy material. However, scientists did not consider that, in the absence of a joke or a remark, laughter by itself can evoke laughter. This is a key element in the propagation of contagious laughter.

I recently performed some investigations of the phenomenon of contagious laughter in an undergraduate psychology classroom. The stimulus was a "laugh box"—a small battery-operated record player from a novelty store—that emitted an 18-second span of laughter. The "canned" laughter was played 10 times, with the beginning of each segment separated by a one-minute interval.

On the first stimulus nearly half of the students reported that they responded with laughter themselves. (More than 90 percent reported smiling on the first stimulus.) However, the effectiveness of the stimulus declined with each repetition until only 3 of the 128 students laughed on the tenth trial. By that point about 75 percent of the students rated the laugh stimulus as "obnoxious."

The negative effect of the repeated stimulus seems to go beyond the response expected from the recurrent exposure to a generic auditory stimulus, such as "Hello, my name is George." The reaction may reflect the deep biological significance of laughter, which in this case may be perceived as jeering or ridicule. (Colleagues whose offices adjoin my own can attest to the aversiveness of periodic canned laughter. Personally, I find myself wincing every time one of the laugh boxes in my office is accidently activated.) Certainly it is pleasurable to laugh at or with people, but it is quite unpleasant to be laughed at, or to be the recipient of a scornful "ha." Court fools and presidential aides learn early in their careers that it is safer to laugh with the boss than at him or her.

The efficacy of laughter alone to elicit laughter raises the intriguing possibility that human beings have auditory "feature detectors"—neural circuits that respond exclusively to this species-typical vocalization. In turn, the feature detector triggers the neural circuits that generate the stereotyped action pattern of laughter. This mechanism, involving a laugh detector that drives a laugh generator, may be the foundation of contagious laughter. (Contagious yawning appears to involve a similar process in the visual domain.) Those who attempt to explain away their laugh-evoked (contagious) laughter as nothing more than a response to a "funny" stimulus are saying that they laughed in response to a stimulus that made them laugh, a circular argument.

The structural simplicity and species-typical character of laughter makes it a prime candidate for the evolution of such a laugh detection and releasing process. Future psychophysical studies must determine which of laughter's parameters—note structure, note duration, internote interval and amplitude dynamics—are necessary for the perception of laughter and the activation of the hypothetical laugh detector or releasing mechanism. Similar detectors may have evolved for universal phonemic features of speech but the variability and complexity of language and the absence of a contagious response to assay the activation of the detectors will make their discovery more difficult.

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