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

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 500Hz) varying over a large range (<30dB HL to >70dB 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+10dB signal-to-noise ratio (SNR) (. n=69), and (iv) AzBio sentences at+5dB SNR (. n=64). We find maximum bimodal benefit when (i) CI scores are less than 60 percent correct, (ii) hearing loss is less than 60dB 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>.