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 noise level by increasing
the number of samples included in the averaged response.
However, improvement achieved in this way assumes that
the signal, the MMN, remains stable for extended test times,
an assumption which has not been 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 to various speech syllable contrasts.
Significant long-term habituation of MMN was observed for
all three subject populations tested: young adults, school-age
children, and guinea pigs. The time course of the habituation
and the stimulus conditions under which it occurs have
important implications for 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.