Evaluation of the Benefits of Bilateral Fitting in Bone-Anchored Hearing System Users: Spatial Resolution and Memory for Speech
Authors: Brassington William , Parker Rosalyn , Bianchi Federica 
Published: November 2022

Objectives:
The purpose of this study was to evaluate the benefits of bilateral implantation for bone-anchored hearing system (BAHS) users in terms of spatial resolution abilities and auditory memory for speech.

Design:
This is a prospective, single-center, comparative, single-blinded study where the listeners served as their own control. Twenty-four experienced bone-anchored users with a bilateral conductive or mixed hearing loss participated in the study. After fitting the listeners unilaterally and bilaterally with BAHS sound processor(s) (Ponto 3 SuperPower), spatial resolution was estimated by measuring the minimum audible angle (MAA) to achieve an 80% correct response via a two-alternative-forced choice task (right-left discrimination of noise bursts) in two conditions: both sound processors active (bilateral condition) and only one sound processor active (unilateral condition). In addition, a memory recall test, the Sentence-final Word Identification and Recall (SWIR) test was performed with five lists of seven sentences for each of the two conditions (unilateral and bilateral). Self-reported performance in everyday life with the listener’s own sound processors was also evaluated via a questionnaire (the abbreviated version of the Speech, Spatial and Qualities of Hearing scale).

Results:
The MAA to discriminate noise bursts improved significantly from 75.04° in the unilateral condition to 3.61° in the bilateral condition (p < 0.0001). The average improvement in performance was 54.28°. The SWIR test results showed that the listeners could recall, on average, 55.03% of the last words in a list of seven sentences in the unilateral condition and 57.23% in the bilateral condition. While the main effect of condition was not significant, there was a significant interaction between condition and repetition (list), revealing a significantly higher recall performance in the bilateral condition than in the unilateral condition for the second repetition/list out of five (10.2% difference; p = 0.022). Self-reported performance with bilateral BAHS obtained via the Speech, Spatial and Qualities of Hearing scale questionnaire was, on average, 4.4 for speech, 3.7 for spatial, and 5.1 for qualities of hearing. There was no correlation between self-reported performance in everyday life and bilateral performance in the MAA test, while significant correlations were obtained between self-reported performance and recall performance in the SWIR test.

Conclusions:
These results showed a large benefit in spatial resolution for users with symmetric BC thresholds when being fitted with two BAHS, although their self-reported performance with bilateral BAHS in everyday life was rather low. In addition, there was no overall benefit of bilateral fitting on memory for speech, despite observing a benefit in one out of five repetitions of the SWIR test. Performance in the SWIR test was correlated with the users’ self-reported performance in everyday life, such that users with higher recall ability reported to achieve better performance in real life. These findings highlight the advantages of bilateral fitting on spatial resolution, although bilaterally fitted BAHS users continue to experience some difficulties in their daily lives, especially when locating sounds, judging distance and movement. More research is needed to support a higher penetration of bilateral BAHS treatment for bilateral conductive and mixed hearing losses.