Introduction: The effect of attention on the processing of auditory sensory input was studied in recordings of the mismatch negativity (MMN), derived from the event-related EEG. Methods: Twenty healthy normal young adults (mean 25.8y) were presented with a series of frequent standard, and rare deviant auditory stimuli in two sessions about 5 weeks apart. Some deviant stimuli were a little different (80 vs. 40 ms or 0.5 vs. 1.0 KHz), others differed considerably from the standards (complex novel sounds). Event-related potential (ERP) recordings were made while subjects responded first on a visual and then on an auditory discrimination task. Results: First: Directing attention intramodally (to the auditory discrimination) resulted in a larger MMN amplitude -- only in the case of low stimulus deviance, and on the first recording session. Second: Directing attention extramodally (to the visual discrimination) did not differentially affect MMN amplitude after the different auditory deviants. Conclusions: Novel stimuli may trigger an involuntary switch of attention, thus overwriting the effects of task-related attentional direction seen with lower degrees of stimulus deviance. However, the effects of task / modality involving the direction of attention on MMN / change detection (Oades & Dittmann-Balcar, 1995) may diminish as task performance becomes more automatic.The potential for differential roles for MMN sources reported in frontal and temporal lobes (Jemel et al., 2002) in the violations of expectation associated with short-term auditory memory are discussed.