Pitch Adaptation Patterns in Bimodal Cochlear Implant Users: Over Time and Long-term

Abstract

Objectives:

(1) Characterize pitch adaptation patterns in bimodal long-electrode cochlear implant (CI) users over time, and correlate these with electrode discrimination and speech perception outcomes. (2) Compare to pitch plasticity observed in hybrid CI users.

Methods:

Observational cohort over a 12-month period after CI activation or of long-term CI experience. Severe to profound hearing impairment in 19 newly activated bimodal CI users and 20 long-term CI users was studied in an audiology clinic. Outcome measures: Electric-to-acoustic pitch matches, audiometric thresholds, electrode discrimination performance, and speech perception scores, measured over time.

Results:

Recently activated (12 months) subjects had these pitch adaptation patterns: pitch-adapting, pitch-dropping, and pitch-unchanging. Long-term subjects had a parallel set of adaptation patterns: matched-pitch, low-pitch, and nonmatched-pitch. Unlike hybrid CI users who are mostly pitch-adapting/matched-pitch, the majority of bimodal CI users demonstrated pitch-dropping/low-pitch or pitch-unchanging/nonmatched-pitch. Subjects with pitch-adapting/matched-pitch patterns trended towards better low-frequency thresholds. Changes in electrode discrimination were not associated with pitch differences between electrodes. Reductions in speech perception scores over time were associated with dropping-pitch patterns.

Conclusions:

Bimodal CI users with more residual hearing seem similar to hybrid CI users in adapting pitch perception to reduce mismatch with the frequencies allocated to the electrodes and acoustic hearing. In contrast, those with less residual hearing exhibit no adaptation or a drop in the pitches of the basal electrodes. Our data suggest that electrode discrimination does not depend on perceived pitch differences between electrodes. Speech perception may depend more on pitch perception and the ability to distinguish pitch between electrodes.