Burrhus Frederic Skinner - Superstition in the pigeon - Encyclopedia II

One of Skinner's most famous and interesting experiments examined the formation of superstition in one of his favorite experimental animals, the pigeon. Skinner placed a series of hungry pigeons in a cage attached to an automatic mechanism that delivered food to the pigeon "at regular intervals with no reference whatsoever to the bird's behaviour". Whatever chance actions each bird had been performing as food was delivered was strengthened, so the bird continued to perform the same actions:

One bird was conditioned to turn anti-clockwise about the cage, making two or three turns between reinforcements. Another repeatedly thrust its head into one of the upper corners of the cage. A third developed a 'tossing' response, as if placing its head beneath an invisible bar and lifting it repeatedly. Two birds developed a pendulum motion of the head and body, in which the head was extended forward and swung from right to left with a sharp movement followed by a somewhat slower return.
—B.F. Skinner (1947). 'Superstition' in the Pigeon. Journal of Experimental Psychology 38.

The experiment might be said to demonstrate a sort of superstition. The bird behaves as if there were a causal relation between its behaviour and the presentation of food, although such a relation is lacking. There are many analogies in human behaviour. Rituals for changing one's luck at cards are good examples. A few accidental connections between a ritual and favourable consequences suffice to set up and maintain the behaviour in spite of many non-reinforced instances. The bowler who has released a ball down the alley but continues to behave as if he were controlling it by twisting and turning his arm and shoulder is another case in point. These behaviours have, of course, no real effect upon one's luck or upon a ball half way down an alley, just as in the present case the food would appear as often if the pigeon did nothing -- or, more strictly speaking, did something else.
—ibid

Adapted from the Wikipedia article "Superstition in the pigeon", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki/Main_Page