MISMATCH NEGATIVITY (MMN) IS ALTERED BY DIRECTING ATTENTION

MMN is a negative component resulting from the difference in event-rel ated potential (ERP) waveforms elicited by a standard and a deviant st imulus. It is usually studied in the absence of attentional requiremen ts. We compared this measure of perceptual comparison in a non-task si tuation (three tones presented) with that obtained in a task requiring focused attention and response to the third tone. MMN (comparison of standard and deviant irrelevant tones) increased with focused attentio n to the third (target) tone and frontal maxima shifted slightly poste riorly. The succeeding P3 in the difference waveform increased more po steriorly than frontally confirming continued differential processing of irrelevant stimuli under active conditions. This demonstrates that not only attending to stimuli, but the active processing of irrelevant stimuli (YS passive perception) involves small changes in the amount and distribution of neural activity.