(Excerpted from "Editors' Choice: Highlights of the recent literature SCIENCE, Volume 318, Issue 5851 dated November 2 2007") To hold two opposed ideas in the mind at the same time and still retain the ability to function has been hailed as the mark of first-rate intelligence--and would also be likely to elicit a state of cognitive dissonance, which arises when beliefs and behaviors collide. Alas, ample evidence indicates that most humans are able and willing to alter their attitudes so as to bring them into line with how they have behaved, and thus to reduce the discordance between the two. In fact, three equally valued items (A, B, and C) can be experimentally manipulated--by asking a subject to choose first between A and B, and then by asking the subject to make a second choice between C and the unchosen item from the first round-to yield a greater than 50% preference for C over A or B. The explanation of this outcome is that the unchosen item has lost value by virtue of not having been selected, and thus suffers in comparison to C.
Egan et al. have adopted this paradigm, using stickers featuring various animals and a spectrum of colored M&Ms, to investigate the existence and resolution of cognitive dissonance in 4-year-old children and capuchin monkeys. They find that both subject pools behave similarly; that is, item C IS indeed chosen significantly more of the time (60%) when subjects have been enticed into a state of cognitive dissonance via a first-round choice of A versus B, and C is not selected more often when the subjects are simply presented in the first round with A or B as the experimenter's choice.