To switch or not to switch: brain potential indices of attentional control after task-relevant and task-irrelevant changes of stimulus features.

Attention is controlled by the interplay of sensory input and top-down processes. We compared attentional control processes during task switching and reorientation after distraction. The primary task was to discriminate laterally and centrally presented tones; these stimuli were composed of a frequent standard or an infrequent deviant pitch. In the distraction condition, pitch was irrelevant and could be ignored. In the switch condition, pitch changes were relevant: whenever a deviant tone was presented, participants had to discriminate its pitch and not its direction. The task in standard trials remained unchanged. In both conditions, deviants elicited mismatch negativity (MMN), P3a, P3b, and reorienting negativity (RON). We, therefore, suggest that distraction and switching are triggered by the same system of attentional control. In addition, remarkable differences were observable between the two conditions: In the switch condition the MMN was followed by a more pronounced N2b and P3a. The differences between these components support the idea that in the distraction condition, a switch of attention is only initiated but not completely performed.