Individual differences in slow brain potentials in a guessing task.

Abstract

18 healthy right-handed subjects had to predict one of two random non-equiprobable events by pressing one of two buttons with the right index finger. Each trial was preceded by a cue that increased the probability of the corresponding event in comparison to its overall probability. The Bereitschaftspotential (BP) before an action and the stimulus-preceding negativity (SPN) between the action and the event presentation were recorded. The subjects were subdivided into groups according to their tendency to follow the cue or to reject it. Cue rejection provided in the present situation a larger final gain than cue acceptance. Those subjects who used the former strategy were characterized by a local BP increase over the right parietal cortex, when a low-probable cue was presented. Their SPN amplitude was relatively small, but it increased substantially after a low-probable cue. Subjects who tended to follow the cue had a very large BP amplitude over the projection area and at vertex. Their SPN was overall large, regardless of condition. Peculiarities of the potentials recorded in these subjects are thought to relate to their desire to minimize errors.