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FEATURE ARTICLE

Laughter

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

Robert Provine

Future Directions

Now that the critical dimensions of laughter as a social stimulus and motor act have been identified, we can pursue a variety of promising issues. Consider "pathological laughter," a frequent and often vaguely described medical symptom. Damage to a wide variety of brain regions produces abnormal laughter, a result consistent with the diverse emotional, respiratory, motor, cognitive and communicative aspects of the act. The most common cases of pathological laughter are found in pseudobulbar palsy, gelastic epilepsy and psychiatric illness. However, pathological laughter has also been reported in multiple sclerosis, amyotrophic lateral sclerosis (Lou Gehrig's disease), and cases of tumors and lesions (especially in the limbic system and the brain stem). Particularly mystifying to both patient and clinician are sudden bursts of laughter that are not associated with a feeling of mirth or an environmental stimulus. Here we have a segregation of the emotional, cognitive and motor mechanisms of laughter. Other cases are more subtle. Some people with forebrain damage have their readjustment to society impeded by a tendency to laugh at almost anything—breaches in laugh etiquette have more serious consequences than one might think. Using our improved descriptive tools, we can now specify more precisely what is "abnormal," "pathological" or "inappropriate" about these cases (whether it is sonic structure, placement in speech, social context, contagion sensitivity, perception or relation to humor). We may even discover new laugh-related syndromes.

The next time that you or a friend have one beer too many, you may research the age-old question of alcohol effects—while taking careful notes on a cocktail napkin, of course. Do alcohol, "laughing gas" and other drugs known to increase laughter simply lower the threshold for laughter, or do they alter its pattern or quality? In aphasia (a disorder of language production or perception) is there sparing of laughter and, if so, which of laughter's several dimensions are spared? Does vocal laughter punctuate the signed speech of the congenitally deaf, in whom there is not a shared organ of expression? The left cerebral hemisphere has a specialized role in language—is this also true of the production or perception of laughter?

Many developmental issues remain open. Laughter typically appears in human babies around 3-1/2 to 4 months of age, but we know little about the details of the developmental process. Must babies hear their own laughter or the laughter of others for laughter to mature? If so, is there a critical period during which such laughter must be experienced? The report of laughter in a few congenitally deaf-blind children suggests that at least some features of laughter develop without benefit of auditory and visual stimulation, evidence of a strong maturational and genetic basis. For a more satisfying account of laugh acquisition, we must conduct high-resolution studies that contrast the development of normal and hearing-impaired children.

All of us have encountered people with bizarre-sounding laughter. What is different about such laughter and what does this tell us about the mechanism of normal laugh production? Do these odd types of laughter run in families? If so, what is the nature of its development and heritability? In my otherwise forgettable high-school physics class there was a kid who brayed like a donkey when he laughed. Where is Roger now that I need him?

Comparative studies may provide clues about both the evolution and social function of laughter. Does the low level of conscious control that we have over our own laughter reflect the typical level of control that non-human animals have over their own species-typical vocalizations? Do the great apes show the sexually dimorphic or contagious laughter described in human beings? Does the pattern of laughter vary with rank within a troop? Aside from the great apes, do other animals produce laugh-like vocalizations? How do the neurobehavioral mechanisms of laugh production vary between species? Tickle may be a kind of Rosetta Stone for such comparative laugh research because it triggers laugh-like vocalizations in all of the great apes and perhaps other species. Can you tickle your pet dog or cat? How can you tell? Is a laugh-evoking stimulus that works equally well in a variety of species the ultimate example of "low" humor?

Laughter research is still in its infancy, an exciting time when the frontiers are near at hand and accessible with modest resources. Certainly much of the research described in this article can be replicated or extended by almost anyone, making it suitable for college or even high school research projects. Laughter research is a reminder that not all science concerns arcane or narrow problems. We should resist neglecting or trivializing the commonplace. There are rewards for approaching nature with a naive curiosity and attempting to see the familiar in new ways.

Bibliography

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  • Provine, R. R. 1986. Yawning as a stereotyped action pattern and releasing stimulus. Ethology 72:109-122.
  • Provine, R. R. 1992. Contagious laughter: Laughter is a sufficient stimulus for laughs and smiles. Bulletin of the Psychonomic Society 30:1-4.
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  • Provine, R. R. In press. Contagious yawning and laughter: Significance for sensory feature detection, motor pattern generation, imitation, and the evolution of social behavior. In Social Learning in Animals: The Roots of Culture, ed. C. M. Heyes and B. G. Galef. New York: Academic Press.
  • Provine, R. R., and K. R. Fischer. 1989. Laughing, smiling, and talking: Relation to sleeping and social context in humans. Ethology 83:295-305.
  • Provine, R. R., and Y. L. Yong. 1991. Laughter: A stereotyped human vocalization. Ethology 89:115-124.
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