Relationships between the auditory nerve’s ability to recover from neural adaptation, cortical encoding of and perceptual sensitivity to within-channel temporal gaps in postlingually deafened adult cochlear implant users

ABSTRACT Objective This study assessed the relationships between the auditory nerve’s ability to recovery from neural adaptation, cortical encoding of and perceptual sensitivity to within-channel temporal gaps in postlingually deafened adult cochlear implant (CI) users. Design Study participants included 11 postlingually deafened adults with Cochlear™ Nucleus® devices, including three bilaterally implanted participants. In each participant, recovery from neural adaptation of the auditory nerve (AN) was measured using electrophysiological measures of the electrically evoked compound action potential (eCAP) at up to four electrode locations. The electrode pair with the largest difference in the speed of adaptation recovery was selected for assessing within-channel temporal gap detection threshold (GDT). GDTs were measured using both psychophysical and electrophysiological procedures. Psychophysical GDTs were evaluated using a three-alternative, forced-choice procedure, targeting 79.4% correct on the psychometric function. Electrophysiological GDTs were measured using the electrically evoked auditory change complex (eACC) evoked by electrical pulse trains that contained temporal gaps. Objective GDT was defined as the shortest temporal gap that could evoke an eACC. Related-samples Wilcoxon Signed Rank testwas used to compare psychophysical GDTs and objective GDTs measured at all electrode locations. It was also used to compare psychophysical GDTs and objective GDTs measured at the two electrode locations with different speeds or amounts of adaptation recovery of the AN. A Kendall Rank correlation test was used to assess the correlation between GDTs measured using psychophysical or electrophysiological procedures. Results Objective: GDTs were significantly larger than those measured using psychophysical procedures. There was a significant correlation between objective and psychophysical GDTs. GDTs could not be predicted based on the amount or the speed of adaptation recovery of the AN. Conclusions Electrophysiological measure of the eACC can potentially be used to assess within-channel GDT in CI users who cannot provide reliable behavioral responses. The difference in adaptation recovery of the AN is not the primary factor accounting for the across-electrode variation in GDT in individual CI users.