The Objective Test of Cochlear Dead Region Using Acoustic Change Complex: A Preliminary Report / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Cochlear dead region (CDR) is a region in the cochlear where hearing loss has occurred due to damage to the inner hair cells and/or neurons. Recently, a subjective test involving a pure-tone test in the presence of threshold-equalizing noise (TEN) was introduced to identify CDR. However, for uncooperative patients, such a subjective method would be unsuitable and objective methods would be needed instead to detect CDR. The acoustic change complex (ACC) is an evoked potential elicited by changes in the ongoing sound. In this study, we developed an objective method of identifying CDR by combining ACC response with a TEN test, namely the TEN-ACC test, and investigated its feasibility in normal-hearing listeners. SUBJECTS AND METHOD: Ten normal-hearing subjects participated in this study. All subjects underwent both behavioral TEN test and electrophysiological TEN-ACC test. The stimuli for the TEN-ACC test consisted of TEN and embedded pure tones with different frequencies/signals to noise ratios (SNRs). To identify the thresholds, the range SNR of stimulation was varied from 0 to 20 dB, in stages of 4 dB. RESULTS: The ACC responses of all subjects who participated in this study were well elicited by stimuli developed for the TEN-ACC test. We confirm that the pure-tones embedded in TEN elicited the objective ACC response. CONCLUSION: The results of this study suggest that the novel TEN-ACC test can be applied to evoke ACC in normal-hearing listeners. Future research should incorporate hearing-impaired listeners to determine the feasibility of the TEN-ACC test as an objective method to identify CDR.

The Relationship between Thresholds of Electrically Evoked Compound Action Potential and Speech Perception in Children with Cochlear Implants / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Neuropathology around the cochlea could create variation from site to site in physiological thresholds of cochlear implant users. This variability would be detrimental to speech recognition with a cochlear implant for a variety of reasons, including distortion of the place code and variation in the number of neurons. The purpose of this study is to examine the relationship between thresholds of electrically evoked compound action potential (ECAP) and speech perception in children implanted with the Nucleus Freedom devices. SUBJECTS AND METHOD: Fifty-seven children implanted with the Nucleus Freedom device participated in this study. ECAP thresholds were recorded using the automated neural response telemetry test protocol. We then calculated mean threshold and three metrics to assess across-site variation within subjects: 1) the variance of T levels for all tested sites, 2) the range of T levels (highest minus lowest) across all tested sites and 3) site-to-site variation. For each subject, these measures were compared with performance on tests of word recognition. RESULTS: There was considerable across-site (within-subject) and across-subject variability in thresholds. However, we found no significant correlation between speech recognition and across-site variation of thresholds as well as mean threshold levels. CONCLUSION: These data suggest that the ECAP measures of thresholds may not be an accurate predictor of speech perception ability.