You can easily make your niece giggle and squirm by tickling her. But no matter how ticklish you are, you can’t tickle yourself. Why not?
What is a tickle?
It’s a sensation between an itch and a brush, yet it can often provoke laughter and a pleasant response. It can play a social role. Your niece may merely giggle because of the sensation, but it could also be due to conditioning – tickling might be a learned way for adults and children to bond, for example. Tickling can also be a form of couples-bonding or sexual foreplay – perhaps the laughter and retreat may be a way of showing some level of submission to your partner.
So why can’t you tickle yourself?
Part of this may be psychological. If social conventions play a role, you may not react because tickling yourself involves no interaction with another person. This is not the whole story, however as studies have shown that tickling by a perceived machine is as effective as tickling by another person.
So it probably comes down to prior knowledge. When you move your hand, your brain accurately predicts the movement and then attenuates or dampens responses at the expected tickle location.
Experiments using a progressively less controllable robotic arm showed that as the ability to predict the touching sensation is reduced, the tickliness increases. When another person (or machine) tickles you, you cannot predict the motion exactly and thus it feels more tickley.
Blakemore SJ, Wolpert D, Frith C (2000) Why can’t you tickle yourself? Neuroreport 11(11):R11-6.
Blakemore SJ, Wolpert DM, Frith CD (1998) Central cancellation of self-produced tickle sensation. Nat Neurosci. 1(7):635-40.
Harris CR, Christenfeld N (1999) Can a machine tickle? Psychon Bull Rev. 6(3):504-10
Selden ST (2004) Tickle J Am Acad Dermatol. 50(1) 93-7