Mismatch negativity: a tool for the assessment of stimuli discrimination in cochlear implant subjects

Objectives: The performance of cochlear implants varies among users. This v ariability may be due to the ability to process auditory information. The m ismatch negativity should provide an index of discrimination in cochlear im plantees (Kraus N, McGee T, Carrell T, Sharma A. Neurophysiologic bases of speech discrimination. Ear Hear. 1995;16:19-37). Our aim was to analyze MMN in cochlear implant (Digisonic) subjects to assess electrode discriminatio n and to study the relationship between MMN and speech performance. Methods: The mismatch was determined by stimulating three pairs of differen t electrodes. Two sessions were performed with both standard and deviant st imuli reversed. Speech recognition abilities were evaluated using 4 speech tests. The statistics included the results of 6 subjects. They indicated th at MMN may be obtained when stimulating two different electrodes. A differe nce occurred between standard and deviant stimuli within a session but also when the response to the deviant stimulus was compared to the response of the same stimulus in a standard condition, validating the discrimination pr ocess. MMN latency was about 140 ms, and amplitude about -2.8 mu V. No diff erences were shown with respect to electrode spacing. No relationship betwe en MMN and speech performance was found. A clinical application of this met hod might be to assess the auditory processing of electrical stimuli in con genitally deaf subjects at the pre-implantation stage. (C) 2000 Elsevier Sc ience Ireland Ltd. All rights reserved.