Sound Localization in Single-Sided Deafness; Outcomes of a Randomized Controlled Trial on the Comparison Between Cochlear Implantation, Bone Conduction Devices, and Contralateral Routing of Signals Hearing Aids

Abstract

There is currently a lack of prospective studies comparing multiple treatment options for single-sided deafness (SSD) in terms of long-term sound localization outcomes. This randomized controlled trial (RCT) aims to compare the objective and subjective sound localization abilities of SSD patients treated with a cochlear implant (CI), a bone conduction device (BCD), a contralateral routing of signals (CROS) hearing aid, or no treatment after two years of follow-up. About 120 eligible patients were randomized to cochlear implantation or to a trial period with first a BCD on a headband, then a CROS (or vice versa). After the trial periods, participants opted for a surgically implanted BCD, a CROS, or no treatment. Sound localization accuracy (in three configurations, calculated as percentage correct and root-mean squared error in degrees) and subjective spatial hearing (subscale of the Speech, Spatial and Qualities of hearing (SSQ) questionnaire) were assessed at baseline and after 24 months of follow-up. At the start of follow-up, 28 participants were implanted with a CI, 25 with a BCD, 34 chose a CROS, and 26 opted for no treatment. Participants in the CI group showed better sound localization accuracy and subjective spatial hearing compared to participants in the BCD, CROS, and no-treatment groups at 24 months. Participants in the CI and CROS groups showed improved subjective spatial hearing at 24 months compared to baseline. To conclude, CI outperformed the BCD, CROS, and no-treatment groups in terms of sound localization accuracy and subjective spatial hearing in SSD patients. TRIAL REGISTRATION Netherlands Trial Register (https://onderzoekmetmensen.nl): NL4457, CINGLE trial.

Keywords: cochlear implantation; follow-up studies; hearing aids; hearing loss; sound localization; unilateral.

Figure 1.

Study flow diagram. See the Appendix for participant allocation at each moment of follow-up. Abbreviations: BCD, bone conduction device; CI, cochlear implant; CROS, contralateral routing of signals hearing aid.

Figure 2.

Sound localization test setup. The setup consisted of a horizontal arch from −90° to +90° with nine loudspeakers. The radius of the loudspeakers to the participant was 1.45 m. Screens were mounted below the loudspeakers were numbers could be presented.

Figure 3.

A-C. Sound localization accuracy calculated as RMS error in degrees per configuration. D-F. Sound localization accuracy calculated as % correct per configuration. The boxplots display the minimum, first quartile, median, third quartile, and maximum. After Bonferroni correction, p-values < 0.017 were considered to be statistically significant. Statistically significant differences between groups at 24 months of follow-up: ** = p < 0.017; *** = p < 0.001. For the statistical difference within groups at 24 months compared to baseline: •• = p < 0.017; ••• = p < 0.001. Abbreviations: BCD, bone conduction device; BLN, baseline; CI, cochlear implant; CROS, contralateral routing of signals hearing aid; RMS, root-mean squared localization error in degrees.

Figure 4.

Response patterns for the 15-degree configuration at baseline, 3, and 24 months of follow-up. The sound source location is indicated on the x-axis, and the response location is indicated on the y-axis. The shading indicates the frequency of each observed stimulus-response pair. The contrast ranges from white at the lowest frequency to black at the highest frequency. Abbreviations: BCD, bone conduction device; CI, cochlear implant; CROS, contralateral routing of signals hearing aid.

Figure 5.

Subjective spatial hearing assessed with the SSQ spatial hearing subscale. The boxplots display the minimum, first quartile, median, third quartile, and maximum. After Bonferroni correction, p-values < 0.017 were considered to be statistically significant. Statistically significant differences between groups at 24 months of follow-up: ** = p < 0.017; *** = p < 0.001. For the statistical difference within groups at 24 months compared to baseline: •• = p < 0.017; ••• = p < 0.001. Abbreviations: BCD, bone conduction device; BLN, baseline; CI, cochlear implant; CROS, contralateral routing of signals hearing aid; SSQ, Speech, Spatial and Qualities of hearing scale.