INTEGRATED MISMATCH NEGATIVITY (MMNI) - A NOISE-FREE REPRESENTATION OF EVOKED-RESPONSES ALLOWING SINGLE-POINT DISTRIBUTION-FREE STATISTICALTESTS

If the repeated presentation of a single (standard) auditory stimulus is randomly interspersed with a second acoustically different (deviant ) stimulus, the cortical activity evoked by the deviant stimulus can c ontain a negative component known as the mismatch negativity (MMN). Th e MMN is derived by subtracting the averaged response evoked by the st andard stimulus from that evoked by the deviant stimulus. When the mag nitude of the response is small or the signal-to-noise ratio is poor, it is difficult to judge the presence or absence of the MMN simply by visual inspection, and statistical detection techniques become necessa ry. A method of analysis is proposed to quantify the magnitude and sta tistically evaluate the presence of the MMN based on time-integrated e voked responses. This paper demonstrates the use of this integrated mi smatch negativity (MMNi) analysis to detect the MMN evoked by stimulus contrasts near the perceptual threshold of two subjects. The MMNi, by virtue of being equivalent to a low-pass filtered response, presents an almost noise-free estimate of MMN magnitude. A single measure of th e integrated evoked response at a fixed time point is used in a distri bution-free statistic that compares the magnitude of the averaged resp onse evoked by the deviant stimulus with a magnitude distribution deri ved from 200 subaveraged responses to the standard stimulus (with the number of sweeps per average equal to that of the deviant stimulus). T his allows a calculation of the exact probability for the null hypothe sis that the negative magnitude of the response evoked by the deviant stimulus is drawn from the magnitude distribution of responses evoked by the standard stimulus. Rejection of this hypothesis provides object ive evidence of the presence of the MMN. (C) 1997 Elsevier Science Ire land Ltd.