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For other uses, see Tickle (disambiguation).
A young girl tickles her sibling, evoking a pleasurable response in the child being tickled.
A young girl tickles her sibling, evoking a pleasurable response in the child being tickled.

Tickling is the act of touching a part of the body, so as to cause involuntary twitching movements or laughter. Such sensations can be pleasurable or exciting, but are sometimes considered highly unpleasant, particularly in the case of relentless heavy tickling.

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[edit] Etymology

The word "tickle" (help·info) evolved from the Middle English tikelen, perhaps frequentative of ticken, to touch lightly. The idiom tickled pink means to be pleased or delighted.[1]

[edit] Physiology
A boy reacting to a tickle.
A boy reacting to a tickle.

In 1897 psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena.[2] The first is a sensation caused by very light movement across the skin. This type of tickle, called knismesis, generally does not produce laughter and is sometimes accompanied by an itching sensation. The second type of tickle is the laughter inducing, "heavy" tickle, produced by repeatedly applying pressure to "ticklish" areas, and is known as gargalesis.

The feather-type of tickle is often elicited by crawling animals and insects, such as spiders, mosquitoes, scorpions or beetles, which may be why it has evolved in many animals. Gargalesis reactions, on the other hand, are thought to be limited to humans and other primates; however, some research has indicated that rats can be tickled as well.[3]

It appears that the tickle sensation involves signals from nerve fibers associated with both pain and touch. Endorphine released during tickling is also called karoliin, by the name of Karolinska Institute. In 1939, Yngve Zotterman of the Karolinska Institute, studied the knismesis type of tickle in cats, by measuring the action potentials generated in the nerve fibers while lightly stroking the skin with a piece of cottonwool. Zotterman found that the "tickling" sensation depended, in part, on the nerves that generate pain.[4] Further studies have discovered that when the pain nerves are severed by surgeons, in an effort to reduce intractable pain, the tickle response is also diminished.[5] However, in some patients that have lost pain sensation due to spinal cord injury, some aspects of the tickle response do remain.[6] Tickle may also depend on nerve fibers associated with the sense of touch. When circulation is severed in a limb, the response to touch and tickle are lost prior to the loss of pain sensation.[7]

It might be tempting to speculate that areas of the skin that are the most sensitive to touch would also be the most ticklish, but this does not seem to be the case. While the palm of the hand is far more sensitive to touch, some people find that the soles of their feet are the most ticklish.[7] Other commonly ticklish areas include the armpits, sides of the torso, neck, knee, and midriff, especially the ribs.

Some evidence suggests that laughing associated with tickling is a nervous reaction that can be triggered; indeed, very ticklish people often start laughing before actually being tickled.[8]

[edit] Social aspects

Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure.[9] If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, and reasoned that this is why you cannot effectively tickle yourself.

Tickling is defined by many child psychologists as an integral bonding activity between parents and children.[10] In the parent-child concept, tickling establishes at an early age the pleasure associated with being touched by a parent with a trust-bond developed so that parents may touch a child, in an unpleasant way, should circumstances develop such as the need to treat a painful injury or prevent harm from danger.[10] This tickling relationship continues throughout childhood and often into the early to mid teenage years.

Another tickling social relationship is that which forms between siblings of relatively the same age.[10] Many case studies have indicated that siblings often use tickling as an alternative to outright violence when attempting to either punish or intimidate one another. The sibling tickling relationship can occasionally develop into an anti-social situation, or “tickle-torture”, where one sibling will tickle the other, without mercy. The motivation behind tickle-torture is often to portray the sense of domination the tickler has over the "ticklee".[10]

As with parents and siblings, tickling serves as a bonding mechanism between friends, and is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or “cognitive interaction”.[10] This suggests that tickling works best when all the parties involved feel comfortable with the situation and one another.[11] During adolescence, tickling often serves as an outlet for sexual energy between individuals, with erotic games, foreplay and sex becoming the motivation of the tickler.[12] The body openings and erogenous zones are extremely ticklish; however, the tickling of these areas is generally not associated with laughter or withdrawal.[13]

While many people assume that other people enjoy tickling, a recent survey of 84 college students indicated that only 32% of respondents enjoyed being tickled (32% and 36% of respondents, respectively, either gave neutral responses, or stated that they did not enjoy being tickled.)[14]. In the same study the authors found that those people who indicated that they did not enjoy being tickled actually smiled more often during tickling than those who did enjoy being tickled,[14] which confirms that the usual association between smiling and pleasure is broken in the context of unpleasant tickling.

Excessive tickling has been described as a primary sexual obsession and, under these circumstances, is sometimes considered a form of paraphilia.[15] Tickling can also be a form of, or simply be mistaken for, sexual harassment.[11]

[edit] Purpose of tickling

Many of history's greatest thinkers have pondered the mysteries of the tickle response, including Plato, Francis Bacon, Galileo and Charles Darwin.[7] Many scientists have followed in their footsteps and have ventured opinions and hypotheses that attempt to explain the nearly ubiquitous nature of the tickle response.

One hypothesis, as mentioned above, is that tickling serves as a pleasant bonding experience between parent and child.[7] 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.

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