Event-related potentials reveal modelling of auditory repetition in the brain

Two auditory event-related potential (ERP) waveforms, mismatch negativity (MMN) and repetition positivity (RP), are sensitive to repetition of auditory stimuli. Increasing repetition of standards produces larger MMN amplitudes to deviant stimuli in an oddball paradigm, known as the memory trace effect, and attributed to increasing strength of the memory trace for standards. RP to standards also increases as a function of repetition in a 'roving' oddball paradigm where the standard changes in pitch following presentation of a deviant tone. As the sensory memory trace representing standard stimuli must be continually updated in the roving paradigm, RP has been proposed to reflect memory trace formation. Given that RP to date has only been observed in roving oddball paradigms, we examined whether RP and the MMN memory trace effect are present in both roving and standard oddball paradigms in 24 young adults (mean age: 22.4±5years). Four, 8, or 16 standards preceded a deviant. We observed RP at Fz in standard ERPs in the roving but not constant paradigm. At mastoid sites, RP was observed in both paradigms. A memory trace effect was not observed at Fz in either paradigm. Our findings suggest that different generator sites in the brain model local and global auditory information with generators of mastoid activity primarily sensitive to local or short term stimulus history of auditory regularities while generators of frontal site activity retain more global information regarding stimulus history over a longer time period.