Effects of Cochlear Implantation on Binaural Hearing in Adults With Unilateral Hearing Loss

Abstract

A FDA clinical trial was carried out to evaluate the potential benefit of cochlear implant (CI) use for adults with unilateral moderate-to-profound sensorineural hearing loss. Subjects were 20 adults with moderate-to-profound unilateral sensorineural hearing loss and normal or near-normal hearing on the other side. A MED-EL standard electrode was implanted in the impaired ear. Outcome measures included: (a) sound localization on the horizontal plane (11 positions, -90° to 90°), (b) word recognition in quiet with the CI alone, and (c) masked sentence recognition with the target at 0° and the masker at -90°, 0°, or 90°. This battery was completed preoperatively and at 1, 3, 6, 9, and 12 months after CI activation. Normative data were also collected for 20 age-matched control subjects with normal or near-normal hearing bilaterally. The CI improved localization accuracy and reduced side bias. Word recognition with the CI alone was similar to performance of traditional CI recipients. The CI improved masked sentence recognition when the masker was presented from the front or from the side of normal or near-normal hearing. The binaural benefits observed with the CI increased between the 1- and 3-month intervals but appeared stable thereafter. In contrast to previous reports on localization and speech perception in patients with unilateral sensorineural hearing loss, CI benefits were consistently observed across individual subjects, and performance was at asymptote by the 3-month test interval. Cochlear implant settings, consistent CI use, and short duration of deafness could play a role in this result.

Keywords: localization; single-sided deafness; spatial hearing.

Figure 1.

Unaided thresholds at the time of study enrollment. Pure-tone thresholds are plotted in dB HL as a function of frequency for individual CI recipients (left panel) and the NH controls (right panel). Symbols indicate thresholds for individual subjects. Circles show data for the normal or near-normal hearing ear, and diamonds show data for the ear with UHL. Thresholds shown for the NH control listeners were based on the ear with the higher mean threshold. Boxplots show the distribution of points: horizontal lines indicate the median, boxes span the 25th to 75th percentiles, and vertical lines span the 10th to 90th percentiles. CI = cochlear implant; UHL = unilateral hearing loss; NH = normal hearing.

Figure 2.

CNC word scores across test intervals for CI recipients. Preoperative testing was performed with a hearing aid, and subsequent assessments were performed with the CI alone. The NH ear was masked at all intervals. Results are plotted in percent correct, and plotting conventions follow those of Figure 1. CNC = consonant-nucleus-consonant.

Figure 3.

Distribution of AzBio sentence recognition scores as a function of masker position in units of percent correct. The abscissa indicates the position of the masker; data obtained for the masker at −90° and 90° for the NH control group were randomly assigned as control data for the NH side and the CI side. Horizontal lines indicate the median, boxes span the 25th to 75th percentiles, vertical lines span the 10th to 90th percentiles, and circles indicate the minimum and maximum values. Box shading reflects the subject group and follow-up interval (for the CI recipients). Within each condition, boxes are ordered by the time point of data collection (preoperative on the left, 12-month on the right), with NH control data on the far right of each cluster. For the CI recipients, preoperative data were collected unaided, and postoperative data were collected with the CI. CI = cochlear implant; NH = normal hearing.

Figure 4.

Derived statistics characterizing localization performance as a function of test interval, with unaided performance indicated at the preoperative interval and performance with the CI indicated for postoperative intervals. Values for the NH control group are shown at the far right of each panel. (a) Overall RMS error, with points representing values for individual subjects. (b) The distribution of side bias, with positive values indicating a bias to localize sound on the side of the NH ear, and negative numbers reflecting a bias to localize sound on the CI side. The side representing the NH ear was randomly selected for the NH control group. CI = cochlear implant; NH = normal hearing.