THE MISMATCH NEGATIVITY IN COCHLEAR IMPLANT USERS

For individuals with severe or profound hearing loss, electrical stimu lation of surviving neural elements by a cochlear implant may partly r estore a sensation of hearing. Determining the extent of restoration b ased on behavioral measures may be difficult, particularly when evalua ting young children or individuals who have little or no experience wi th normal hearing. In normal-hearing individuals, an objective measure of sound discrimination may be obtained by studying the mismatch nega tivity (MMN) component of the auditory evoked potential. The MMN may b e evoked by a number of physical differences in acoustic stimuli inclu ding duration and pitch. For cochlear implant users, analogous stimulu s differences may be produced by changing the length of a stimulus pul se train or by changing the pair of activated electrodes along a multi -electrode implant array. This paper will provide an overview of our c urrent results, comparing evoked response data recorded from both norm al-hearing individuals and cochlear implant users. In both normal-hear ing individuals and cochlear implant users, MMNs were evoked by differ ences in stimulus train duration and pitch (or electrode pair activati on in cochlear implant users). These findings suggest that the MMN may be a useful method for assessing the discriminability of electrical s timulation patterns produced by a cochlear implant. Eventually, inform ation gained by MMN testing may yield important information for develo ping rehabilitation programs for the individual user.