Extracting rules: early and late mismatch negativity to tone patterns.

The auditory processing of physical stimulus features can be measured by the mismatch negativity. Past studies have shown that higher-order stimulus features also elicit a mismatch negativity. In some studies, a second component, termed late mismatch negativity, has been observed; yet the functional significance of this component remains unclear. We tested two-tone-pattern stimuli following an abstract rule in healthy adults. As expected, the tone pattern elicited a significant mismatch negativity peaking at 146 ms but a significant late mismatch negativity at around 340 ms was also observed. These findings show that the violation of an abstract rule elicits an early and late mismatch negativity. The late mismatch negativity might be triggered on the basis of auditory rule extraction processes and reflect a transfer of rules to the long-term memory.