Factors constraining the benefit to speech understanding of combining information from low-frequency hearing and a cochlear implant

Abstract

Many studies have documented the benefits to speech understanding when cochlear implant (CI) patients can access low-frequency acoustic information from the ear opposite the implant. In this study we assessed the role of three factors in determining the magnitude of bimodal benefit - (i) the level of CI-only performance, (ii) the magnitude of the hearing loss in the ear with low-frequency acoustic hearing and (iii) the type of test material. The patients had low-frequency PTAs (average of 125, 250 and 500 Hz) varying over a large range (<30 dB HL to >70 dB HL) in the ear contralateral to the implant. The patients were tested with (i) CNC words presented in quiet (n = 105) (ii) AzBio sentences presented in quiet (n = 102), (iii) AzBio sentences in noise at +10 dB signal-to-noise ratio (SNR) (n = 69), and (iv) AzBio sentences at +5 dB SNR (n = 64). We find maximum bimodal benefit when (i) CI scores are less than 60 percent correct, (ii) hearing loss is less than 60 dB HL in low-frequencies and (iii) the test material is sentences presented against a noise background. When these criteria are met, some bimodal patients can gain 40-60 percentage points in performance relative to performance with a CI. This article is part of a Special Issue entitled <Lasker Award>.

Copyright © 2014 Elsevier B.V. All rights reserved.

Figures

Figure 1

Group mean thresholds in dB HL for three groups of listeners. Filled circles indicate thresholds for group 0-40 dB, grey filled squares are for group 41-60 dB and open circles are for group ≥ 61 dB. Symbols are offset slightly on the x-axis to aid reading.

Figure 2

Percentage point benefit in speech understanding for three groups of listeners when tested with CNC words, AzBio sentences in quiet, AzBio sentences at +10 dB SNR and AzBio sentences at +5 dB SNR. Dotted lines indicate 95 percent critical difference scores for the test material. The solid diagonal line indicates the maximum possible score.