Brain responses to number sequences with and without active task requirement

Objective: To examine the effect of the active task involvement versus the passive knowledge of the structure of the stimulation on event-related potentials (ERPs) to violation in number sequences. This should contribute to future development of an ERP test for neurological patients. Methods: ERPs were recorded in subjects who listened to 4-item sequences Of numbers incrementing by one. Half of the sequences had an appropriate end item, whereas the other half ended inappropriately. The role of active versus passive condition v a,, investigated in a between subject design. Results: Incorrectly ending sequences yielded a large P300 wave in all groups. Subjects who were explicitly informed about the nature of the stimulation but did not have a motor task displayed a slow negativity which followed P300 and slightly Suppressed it. In addition, incorrect sequence endings elicited an early (70-200 ms) negativity at frontal sites. This effect was inverted on mastoids. Conclusions: Auditory perception of 3 consecutive numbers constituting a simple incrementing row lead,, to building a strong expectancy concerning the subsequent number, and unexpected events are detected already after the initial phoneme. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.