Relationship between auditory perception skills and mismatch negativity recorded in free field in cochlear-implant users

This study investigated the ability of cochlear-implanted patients to discriminate tone bursts in free field using the electrophysiological recordings of mismatch negativity (MMN). Seven cochlear-implanted patients (CIP) and eight control subjects (CS) were tested. Event-related potentials were recorded from either 32 or 64 electrodes in response to binaural stimuli using a passive oddball paradigm. Two stimulus-contrast conditions were used to produce MMN: The standard-tone frequency was fixed at 1 kHz, and the deviant-tone frequency was set at 2 or 1.5 kHz. The results show that response waveforms (N1/P2) are similar in latency and amplitude for CS and CIP, suggesting that pure-tone detection is performed over the same time window in both groups. These waveforms are also similar in left- and right-implanted patients, suggesting that electric stimulation of the auditory nerve activates both hemispheres in profound, bilateral hearing loss. Pure-tone audiograms and word-discrimination scores were also measured in each subject in an anechoic room and their relations with MMN data were examined. Correlations were found between the latency of MMN for a 1.5 kHz deviant and the thresholds obtained for pure-tone detection and word discrimination. MMN appears as a possible complementary clinical tool to objectively assess auditory sensitivity in cochlear-implanted populations. However, further improvements are still necessary before it can be used as a standard clinical examination.