As part of an experiment, Sally is asked to write an essay advocating an opinion that is opposite to her own. She is given a very small financial incentive to do this ($1) and after completing the essay, the experimenters find that her prior attitude has shifted towards the one advocated in the essay she just wrote. The opinions of other participants in the study who received a larger financial incentive ($50) for writing a counter-attitudinal essay did not show similar shifts. This example best demonstrates the phenomenon called: