The role of large-scale memory organization in the mismatch negativity event-related brain potential

The mismatch negativity (MMN) component of event-related brain potentials i s elicited by infrequent changes in regular acoustic sequences even if the participant is not actively listening to the sound sequence. Therefore, the MMN is assumed to result From a preattentive process in which an incoming sound is checked against the automatically detected regularities of the aud itory sequence and is found to violate them. For example, presenting a disc riminably different (deviant) sound within the sequence of a repetitive (st andard) sound elicits the MMN. In the present article, we tested whether th e memory organization of the auditory sequence can affect the preattentive change detection indexed by the MMN. In Experiment 1, trains of six standar d tones were presented with a short, 0.5-sec stimulus onset asynchrony (SOA ) between tones in the train. This was followed by a variable SOA between t he last standard and the deviant tone (the "irregular presentation" conditi on). Of 12 participants displaying an MMN at the 0.5-sec predeviant SOA, it was elicited by 11 with the 2-sec predeviant SOA, in 5 participants with t he 7-sec SOA, and in none with the 10-sec SOA. In Experiment 2, we repeated the 7-sec irregular predeviant SOX condition, along with a "regular presen tation" condition in which the SOA between any two tones was 7 sec. MMN was elicited in about half of the participants (9 out of 16) in the irregular presentation condition, whereas in the regular presentation condition, MMN was elicited in all participants. These results cannot be explained on the basis of memory-strength decay but can be interpreted in terms of automatic , auditory preperceptual grouping principles. In the irregular presentation condition, the close grouping of standards may cause them to become irrele vant to the mismatch process when the deviant tone is presented after a lon g silent break. Because the MMN indexes preattentive auditory processing, t he present results provide evidence that large-scale preperceptual organiza tion of auditory events occurs despite attention being directed away from t he auditory stimuli.