Visual mismatch negativity to irrelevant changes is sensitive to task-relevant changes.

Event-related potentials (ERPs) were measured in response to frequent (standard) and infrequent (deviant) task-irrelevant bar patterns. The constituent bars of the deviant patterns had either different orientation or different color than the bars of the standard. The task was the detection of either the orientation or the color change of a centrally presented shape. The deviant minus the standard ERP difference produced posterior negativity and was identified as visual mismatch negativity (vMMN). On the one hand, vMMN to orientation deviancy had smaller amplitude in the task demanding detection of the orientation change, and vMMN to color deviancy had smaller amplitude in the task demanding the color change. On the other hand, irrelevant deviancy influenced the task-performance. Reaction time (RT) to the orientation change of the target shape was longer in sequences with orientation change in the background, whereas RT to color change was longer in sequences with color change in the background. This interaction suggested that there was competition between the processing of irrelevant stimuli that share characteristics of task-related changes and target-related processing.