On average, patient speech recognition levels across different cochlear implant (CI) systems are highly similar, yet large outcome variation is observed across patients with the same device. These results indicate significant patient-dependent factors influence speech recognition in CI recipients. We have noted physiological evidence of an ectopic site of electrical stimulation that may produce competing neural activity and may be associated with diminished performance. The physiological observation is the presence of systematic latency shifts of intracochlear evoked potentials across different recording sites for stimulation on a fixed electrode. Subjects presenting with this phenomenon often report competing noise and grunt/echo-like sounds which occur when someone is speaking and are annoying and/or disruptive to speech recognition. The latency-shift phenomenon is observed most often with stimulation on apical contacts of CI users with average-to-poor speech recognition. Based on these and other results, we hypothesize that there are two, spatially-separate sites of excitation which may occur during stimulation with a CI device during typical use. The primary goals in this exploratory two-year project are to test specific predictions of the ectopic excitation site hypothesis and to evaluate alternative stimulation methods which may minimize the occurrence of ectopic excitation. These data will provide new information about the effects of peripheral deficits on patient performance and alternative optimization parameters that may improve the outcomes of CI recipients. The work is organized along three specific aims, including (1) to test the hypothesis that subjects with a greater number of electrodes eliciting ectopic excitation in the apical cochlea have lower speech recognition scores, independent of device type;(2) to test the ectopic excitation hypothesis by examining the effects of various stimulus modes on enhancing and/or diminishing ectopic excitation, by testing for predicted latency shifts of neural responses at brainstem relay nuclei, and correlating anatomical variation with the incidence of signs of ectopic excitation;and (3) to evaluate whether stimulation modes identified to minimize ectopic activation improve speech recognition when incorporated into pulsatile-based speech processing strategies.
This project will increase knowledge of patient-specific, physio-anatomical characteristics that may largely determine or limit outcome level in individual cochlear implant patients. This knowledge will lead to patient-specific fitting strategies and custom sound processor designs which best match information coding to the nature of the electrode nerve interface. Specifically, this project will focus on the occurrence of a secondary ectopic site of neural activation that may occur during electrical stimulation with a cochlear implant. The mechanisms of generation and consequences of its occurrence on speech recognition will be explored. Finally, procedures designed to prevent the occurrence of ectopic stimulation will be evaluated.
| Holden, Laura K; Finley, Charles C; Firszt, Jill B et al. (2013) Factors affecting open-set word recognition in adults with cochlear implants. Ear Hear 34:342-60 |
