DOES IT TICKLE YOUR FANCY?; RESEARCHERS SAY CURIOUS CACKLES HAVE NO HUMOR.

Byline: Carol Kaesuk Yoon The New York Times

It is an enduring mystery pondered over the ages by such luminaries as Socrates, Galileo and Darwin, as well as by many a preschooler: Why do people laugh when they are tickled? Yet tickling has remained little more than a cackle-filled curiosity far from the purview of modern science.

Now a handful of researchers are approaching the subject cautiously and with due scientific gravity, shedding light on why people cannot tickle themselves and why humans evolved to laugh at all. Armed with such unlikely tools as ``tickle machines'' and videotapes of ``Saturday Night Live,'' the scientists are finding that ticklish laughter is not the happy phenomenon that many have assumed it to be.

``Everyone has wondered why we laugh and smile when we're tickled,'' said Christine Harris, a graduate student at the University of California at San Diego who is one of the few researchers in the field. ``It's actually quite bizarre that someone rubbing their fingers up and down your sides or foot makes you laugh.''

She and Dr. Nicholas Christenfeld at the university in San Diego are the authors of two new studies, the first of which was published in a recent issue of the journal Cognition and Emotion.

Dr. Alan Fridlund, a tickle researcher who is a psychologist at the University of California, Santa Barbara, said, ``This is uncharted territory.''

In the late 1800s Charles Darwin and German physiologist Ewald Hecker began some of the first detailed theorizing about tickling. Their combined speculation, now known as the Darwin-Hecker hypothesis, suggested that humor and tickling share deep underlying similarities. Both produce laughter, goosebumps and convulsive muscle contractions; and both, they suggested, appear to require a pleasant state of mind.

To test the hypothesis, Harris and Christenfeld enlisted 72 undergraduates at their university. The basis for the newly published study is what is known as the warm-up effect, the scientific underpinnings for the phenomenon of the warm-up comedian. If a person finds something funny, researchers have previously shown, the next thing encountered will seem that much funnier because of an already giddy state.

So one group of students was tickled for 10 seconds, or until the tickling became intolerable, and then shown videotapes of stand-up comedy routines and clips from ``Saturday Night Live.'' A second group watched the comedy video first and then was tickled. A control group watched a patently unfunny nature video, then was tickled.

Researchers postulated that if humor and tickling are related, and the warm-up effect applies to both, then subjects should laugh more when tickling follows humor or humor follows tickling. But that was not the case. Tickling, the study suggests, does not create a pleasurable feeling - just the outward appearance of one.

Harris said the finding that ticklish laughter did not indicate mirth corroborated the experiences of many people, including herself. ``My second cousins did tickle torture, and I do remember laughing, even though I found it unpleasant,'' said Harris, who describes herself as moderately ticklish.

In fact, in the researchers' latest, still unpublished study employing a so-called tickle machine, they found that far from being the jolly social interaction that many people had assumed it to be, ticklish laughter may be a simple reflex.

Researchers blindfolded 32 undergraduates and told them that a person and a machine would tickle them on the feet, each for five seconds. However, the tickle machine actually did nothing. It looked plausible, with a robotic hand attached to a hose, which was attached to a metal box, on top of which were control panels with lights and buttons and inside of which was a nebulizer, a noisy, vibrating machine used by asthmatics. But in reality, both times students were tickled by a person.

Even when students believed they were alone and being tickled by the machine, they smiled, laughed and wiggled as much as when they knew it was a person. Ticklish laughter, Harris concludes, rather than being social interaction, appears to be a reflex, much the same as the one a doctor elicits from a patient's knee with a little rubber hammer.

The findings corroborate one of the few earlier tickle studies, published in 1941 in the Journal of Genetic Psychology by Dr. Clarence Leuba at Antioch College in Yellow Springs, Ohio. Experimenting on his own two children, he tickled the infants only while wearing a mask, and never in playful situations. Nonetheless, his children laughed when tickled, suggesting that laughter was an innate reflex rather than a learned, social response. (How these children fared later in life is not known.)

But if tickling is indeed a reflex, that raises an even more perplexing question: Why can't people tickle themselves? Harris suggests that it may be the same reason that people cannot startle themselves. What is missing is the element of surprise.

Can't do it alone

Despite the new study, Fridlund contends that people cannot tickle themselves because ticklish laughter is social and requires a tension that can only be created between two or more people in much the same way as with a joke.

If the new studies are correct and ticklish laughter is an innate reflex, this raises the most intriguing question of all: Why should humans have evolved to titter when tickled?

Tickling and laughter are universal among humans and can even be found among chimpanzees, suggesting that they serve some serious evolutionary purpose. Researchers agree that tickling plays an important role in the bonding of infants and parents. Mother tickles baby. Baby laughs and smiles. Mother laughs and smiles. They endear themselves to each other to their mutual evolutionary advantage.

But Dr. Glenn Weisfeld, a human ethologist at Wayne State University in Detroit, suggests that tickling may do much more. Tickling, he maintains, is an educational activity.

``The structures of the body that are most vulnerable to tickling are also the ones that are most vulnerable to attack,'' Weisfeld said. ``We may be responsive to tickling because it gives us practice in defending ourselves.'' Children laugh, he said, to encourage adults to continue this tickle schooling, in what are typically safe, practice play attacks.

For Weisfeld, the notion of the edifying tickle is just part of his theory that all humor provides people with useful information. Slapstick teaches how not to behave. Puns and word play teach about relationships of words, language and concepts. People laugh at jokesters to encourage these teachers to continue their valuable lessons.

Dr. Richard Alexander, the Hubbell professor of evolutionary biology at the University of Michigan in Ann Arbor, views humor in a much bleaker evolutionary light. He suggests that all forms of humor, including tickling, raise the social status of the joke teller or tickler, an elevation that could ultimately increase reproductive success.

Put-down humor, he says is the most obvious example. One person or group is the butt of the joke, lowering their status as the joke teller's is raised. More subtle are intellectual word plays that, Alexander suggests, can raise the social status of the joke teller by showing how clever he or she is and can likewise alter the status of listeners by their ability or inability to understand such intellectual games.

Such thinking sheds new light on that cultural phenomenon, the Tickle-Me Elmo doll and the pleasure derived from making it giggle and squirm. ``Why is the doll so popular?'' Harris asked. ``If it tickled you, it wouldn't be so popular.''

Alexander said: ``A child can be transformed from laughter into tears by going the tiniest bit too far with tickling, raising the question of whether tickling is an expression of dominance. There are lots of people who do abusive tickling, causing great mental pain, and that raises a big question about laughter.''

Alexander offers his dominance theories as speculation, but by thinking back to being trapped in a writhing, sibling heap in the family den yelling ``Uncle!'' it is easy to see tickling as more than a laughing matter.

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5 Photos

PHOTO (1 -- 4) Madison Crane gets the affectionate tickle treatment from her grandmother Frances Lopez. While laughter and tickling go together, new research shows that humor doesn't play a role.

(5 -- cover -- color) Anatomy of a tickle

David R. Crane/Daily News