Long-term habituation of the speech-elicited mismatch negativity

A significant issue in the use of the mismatch negativity evoked potential (MMN) concerns its low signal-to-noise ratio (SNR). One can improve the noi se level by increasing the number of samples included in the averaged respo nse. However, improvement achieved in this way assumes that the signal. the MMN, remains stable for extended test times, an assumption which has not b een tested. If the MMN is not stable, or exhibits habituation over the test session, then SNR would be adversely affected. MMN response magnitude was measured in 5-min intervals over the course of a test session in response t o various speech syllable contrasts. Significant long-term habituation of M MN was observed for all three subject populations tested: young adults, sch ool-age children, and guinea pigs. The time course of the habituation and t he stimulus conditions under which it occurs have important implications fo r research and clinical applications of the MMN. Recording procedures that minimize habituation effects may be used to advantage to improve the signal -to-noise ratio of the MMN.