NEW YORK, Feb 11 (Reuters) -- Scientists may have discovered that the act of tickling has, well, no sense of humor.
"Tickle responses should be viewed as reflexive in nature," say University of California, San Diego (UCSD) researchers. They say that laughter elicited from an episode of "Seinfeld" or a Marx Brothers movie has a different source than that from being tickled. "Tickle and humor responses (share) a common motor-response pathway, without sharing the same psychological state."
Great minds from Socrates to Galileo to Darwin have all asked the question, why do we laugh when tickled? Now, two UCSD studies may have giggled their way to an answer.
One study sought to discover if tickling was at all akin to humor. Researchers had 72 undergraduate students participate in one of three groups. One group watched a video -- "The Best of Saturday Night Live" -- followed by tickling. The second group was tickled first, and then watched the same comedy video. A third group viewed a more sedate nature video, followed by tickling. Subjects were videotaped, and their duration of laughter and smiling was recorded.
The researchers' theory was that, if tickling was related to humor, tickling might serve the same function as a 'warm-up' act at a comedy club, raising the overall level of mirth for the shows' duration. "One might expect that watching a funny film should increase laughter and smiling to subsequent tickle, and vice versa," they surmised.
But the researchers found "there was no difference in seconds spent laughing and smiling as a function of previous tickle.... Having just been tickled did not make the comedy film funnier."
They also point out that, unlike humorous situations, tickling is never sought out by the tickled. The subjects, "Despite agreeing to participate in a tickle study, and despite smiling and laughing... reported that they did not find the experience at all positive." One participant even labeled the study "torture."
And yet researchers note that millions pay to laugh at the latest Robin Williams comedy. "If tickle produced the same positive internal state of mirth," say study authors, "they could just stay at home and tickle one another."
The other UCSD study sought to discover if the social, interpersonal aspect of tickling was intrinsic to the laughing response, since it remains a mystery as to why we cannot tickle ourselves. Researchers set up a mock tickling machine, built to mimic the human hand. "If tickling is fundamentally social," they speculated, "then we should expect that people will not readily laugh and smile when they believe a machine is responsible for producing the tactile stimulation." "Believe" was the operative word in this study, since the machine 'hand' was, in fact, not used, but replaced by the hand of a research assistant who tickled each subjects' foot while hidden under a table out of view of the subject. None of the 34 study subjects "suspected that the tickle machine was not real," according to researchers.
The results of that study? "The belief that a machine or a person is performing the tickling has no effect on how much subjects laugh and smile when tickled." "We wanted to see whether people, who thought they were alone and were being tickled by a machine, would still laugh. They did," said UCSD psychology graduate student and study co-author Christine Harris. "So basically, there was no effect of the social situation."
"The results... leave open the possibility that tickle shares an internal state with other emotions such as social anxiety, and that ticklish laughter might be similar to nervous -- rather than mirthful -- laughter," write the study authors.
So, if it's not humorous, and it's not even social, what is the tickle response? A simplex reflex, researchers conclude. "An analogy would be crying," Harris explained. "There's crying at a funeral and crying from cutting onions. Although there's a common physiological reaction between the two types of tears, you don't think of them as at all similar. The only thing shared is the facial expression."
SOURCE: Cognition and Emotion (1997;10)
