Comparison of Speech Discrimination in Noise and Directional Hearing With 2 Different Sound Processors of a Bone-Anchored Hearing System in Adults With Unilateral Severe or Profound Sensorineural Hearing Loss

Abstract

To evaluate and compare the benefit of a bone-anchored hearing implant with 2 different sound processors in adult patients with unilateral severe to profound sensorineural hearing loss (UHL). Prospective crossover design. Tertiary referral center. Eleven adults with UHL and normal hearing in the contralateral ear were assigned to 2 groups. All subjects were unilaterally implanted with a bone-anchored hearing implant and were initially fitted with 2 different sound processors (SP-1 and SP-2). SP-1 is a multichannel device equipped with an omnidirectional microphone and relatively simple digital signal-processing technology and provides a user-adjustable overall gain and tone control with compression limiting. SP-2 is a fully channel-by-channel programmable device, which can be set with nonlinear dynamic range compression or linear amplification. In addition, SP-2 features automatic noise management, an automatic multichannel directional microphone, microphone position compensation, and an implementation of prescription rules for different types of hearing losses, one of them unilateral deafness. After at least 1-month use of the initial processor, both groups were fitted with the alternative processor. Speech discrimination in noise and localization tests were performed at baseline visit before surgery, after at least 1-month use of the initial processor, and after at least 2-week use of the alternative processor. Relative to unaided baseline, SP-2 enabled significantly better overall speech discrimination results, whereas there was no overall improvement with SP-1. There was no difference in speech discrimination between SP-1 and SP-2 in all spatial settings. Sound localization was comparably poor at baseline and with both processors but significantly better than chance level for all 3 conditions. Patients with UHL have an overall objective benefit for speech discrimination in noise using a bone-anchored hearing implant with SP-2. In contrast, there is no overall objective benefit from SP-1. Depending on the speech-in-noise presentation setting, the difference between objective benefit from SP-2 and SP-1 might be mainly attributed to the new technological features in SP-2 unavailable in SP-1 such as 1) automatic noise management reducing the noise in the speech signal and thus improving the signal-to-noise ratio of the resulting signal on the better ear, 2) programmable multichannel sound-processing and nonlinear dynamic range compression offering considerably greater control over signal amplification compared to SP-1, and 3) implementation of a prescription rule for unilateral deafness addressing the specific amplification needs of patients with UHL by reducing amplification in the low frequencies and applying additional gain in the high frequencies. Sound localization is poor but better than chance level in the unaided condition as well as in both bone-anchored hearing system-aided conditions.