Risk-taking and the human bereitschaftspotential.

The effects of response probability and feedback predictability on the human Bereitschaftspotential (BP) were examined in a probability-matching paradigm. The subjects were to guess, by pressing one of two buttons, which of two possible feedback lights could be lighted. The a priori probabilities (30%-70%) of the feedback were known to the subjects. This task was performed both when the feedback was unpredictable and when it was perfectly predictable from the prior information. The BP was enhanced only when the subjects guessed the improbable feedback when it was unpredictable, thereby putting themselves 'at risk.' This effect seemed to be independent of any concurrent contingent negative variation. The results indicate that the BP is sensitive to trial-by-trial variation of the psychological state, which is in some way related to intention.