Editing Tickling (section)

==Purpose==
Some of history's greatest thinkers have pondered the mysteries of the tickle response, including [[Plato]], [[Francis Bacon]], [[Galileo Galilei]] and [[Charles Darwin]].<ref name=Harris/> In ''[[The Assayer]]'', Galileo philosophically examines tickling in the context of how we perceive reality:<ref>{{cite web|title=Discoveries and Opinions of Galileo|url=http://www.princeton.edu/~hos/h291/assayer.htm|author=Drake, Stillman|publisher=Doubleday & Co.|location=New York|year=1957|page=275|access-date=2008-11-10}}</ref><blockquote>
When touched upon the soles of the feet, for example, it feels in addition to the common sensation of touch a sensation on which we have imposed a special name, "tickling." This sensation belongs to us and not to the hand... A piece of paper or a feather drawn lightly over any part of our bodies performs intrinsically the same operations of moving and touching, but by touching the eye, the nose, or the upper lip it excites in us an almost intolerable titillation, even though elsewhere it is scarcely felt. This titillation belongs entirely to us and not to the feather; if the live and sensitive body were removed it would remain no more than a mere word.</blockquote>

[[Francis Bacon]] and [[Charles Darwin]] believed that humorous laughter requires a "light" frame of mind. But they differed on ticklish laughter: Darwin thought that the same light state of mind was required, whereas Bacon disagreed. When tickled, noted Bacon, "men even in a grieved state of mind, yet cannot sometimes forbear laughing."<ref>Darwin, C. 1872/1965. ''The Expressions of the Emotions in Man and Animals''. London: John Murray.</ref>

One hypothesis, as mentioned above, is that tickling serves as a pleasant bonding experience between parent and child.<ref name=Harris/> However, this hypothesis does not adequately explain why many children and adults find tickling to be an unpleasant experience. Another view maintained is that tickling develops as a prenatal response and that the development of sensitive areas on the fetus helps to orient the fetus into favourable positions while in the womb.<ref>Simpson JY. ''On the attitude of the fetus in utero''. Obstetric Memoirs, vol ii. Philadelphia: Lippincott; 1855–1856.</ref>

It is unknown why certain people find areas of the body to be more ticklish than others; additionally, studies have shown that there is no significant difference in ticklishness among the [[gender]]s.<ref name=Weinstein>Weinstein, S. 1968. "Intensive and extensive aspects of tactile sensitivity as a function of body part, sex, and laterality." In ''The Skin Senses'', ed. D. R. Kenshalo. Springfield, Ill.: Thomas. pp. 195–222.</ref>
In 1924, J. C. Gregory proposed that the most ticklish places on the body were also those areas that were the most vulnerable during hand-to-hand [[combat]]. He posited that ticklishness might confer an [[evolution]]ary advantage by enticing the individual to protect these areas. Consistent with this idea, [[University of Iowa]] psychiatrist Donald W. Black observed that most ticklish spots are found in the same places as the protective [[reflex]]es.<ref>{{cite journal |author=Black DW |title=Laughter |journal=JAMA |volume=252 |issue=21 |pages=2995–2998 |year=1984 |pmid=6502861 |doi=10.1001/jama.252.21.2995}}</ref>

A third, hybrid hypothesis, has suggested that tickling encourages the development of combat skills.<ref name=Harris/> Most tickling is done by parents, siblings and friends and is often a type of rough-and-tumble play, during which time children often develop defensive and combat moves. Although people generally make movements to get away from, and report disliking, being tickled, laughter encourages the tickler to continue. If the facial expressions induced by tickle were less pleasant the tickler would be less likely to continue, thus diminishing the frequency of these combat lessons.

To understand how much of the tickle response is dependent on the interpersonal relationship of the parties involved, [[Nicholas Christenfeld|Christenfeld]] and Harris presented subjects with a "mechanical tickle machine". They found that the subjects laughed just as much when they believed they were being tickled by a machine as when they thought they were being tickled by a person.<ref>Harris, C. R., and N. Christenfeld. In press. ''Can a machine tickle?'' Psychonomic Bulletin and Review.</ref> Harris goes on to suggest that the tickle response is reflex, similar to the [[startle reflex]], that is contingent upon the element of surprise.<ref name=Harris/>