The World's Fair

It begins:

"It has been observed at least since the time of Aristotle that people cannot tickle themselves, but the reason remains elusive."

What we have here is a research paper (by CHRISTINE R. HARRIS and NICHOLAS CHRISTENFELD) that looks at a variety of hypotheses (namely two called the reflex and the interpersonal)on this phenomenon, and then attempts to discern the two by using a "tickling machine." Here's the rest of the abstract:

Two sorts of explanations have been suggested. The interpersonal explanation suggests that tickling is fundamentally interpersonal and thus requires another person as the source of the touch. The reflex explanation suggests that tickle simply requires an element of unpredictability or uncontrollability and is more like a reflex or some other stereotyped motor pattern. To test these explanations, we manipulated the perceived source of tickling. Thirty-five subjects were tickled twice--once by the experimenter, and once, they believed, by an automated machine. The reflex view predicts that our "tickle machine" should be as effective as a person in producing laughter, whereas the interpersonal view predicts significantly attenuated responses. Supporting the reflex view, subjects smiled, laughed, and wiggled just as often in response to the machine as to the experimenter. Self-reports of ticklishness were also virtually identical in the two conditions. Ticklish laughter evidently does not require that the stimulation be attributed to another person, as interpersonal accounts imply.

The entire paper is here(in pdf format) for you to take a look at, but I thought the Apparatus and Materials section in the Methodology was worth sharing additionally (i.e. how to build a tickling machine).

The tickle machine was designed to look and sound like a robotic hand that was capable of movement without the experimenter's assistance. The hand was attached by a long flexible hose to an impressive array of equipment that could plausibly control its motion. This equipment, when turned on, produced a vibrating sound that could be that of a genuine robotic apparatus.

You know, I'd be real curious to see what the grant application looked like for this type of research...