An alternative baseline measure for calculation of the mismatch negativity (MMN) component of the event-related potential (ERP).

Mismatch negativity (MMN), a component of the event-related potential, reflects the processing associated with low-probability (deviant) stimuli over and above that required for high-probability (standard) stimuli. Occurring 100-250 ms post stimulus, MMN is evident in the enhanced negativity generated in response to deviant relative to standard stimuli. Traditionally, the MMN waveform is calculated by subtracting the averaged waveform of all standard stimuli from the averaged waveform of all deviant stimuli collected during the same test session. To investigate whether an unbroken, extended string of standard stimuli may minimize baseline processing, thereby resulting in a more robust measure of MMN, 11 participants were exposed to two contiguous blocks of 1000 trials, each beginning with 60 uninterrupted standard stimuli followed by 940 randomized standard and deviant trials. Negativity related to standard stimuli was minimized in the average of uninterrupted standard stimuli from the second block of trials only while negativity related to uninterrupted standards in the first block of trials was increased relative to all other conditions. The present findings suggest that a familiar, uninterrupted string of standard stimuli, presented midway through an experimental session, may provide a useful alternative baseline for the calculation of MMN.