A longitudinal study in adults with sequential bilateral cochlear implants: time course for individual ear and bilateral performance

Abstract

Purpose: The purpose of this study was to examine the rate of progress in the 2nd implanted ear as it relates to the 1st implanted ear and to bilateral performance in adult sequential cochlear implant recipients. In addition, this study aimed to identify factors that contribute to patient outcomes.

Method: The authors performed a prospective longitudinal study in 21 adults who received bilateral sequential cochlear implants. Testing occurred at 6 intervals: prebilateral through 12 months postbilateral implantation. Measures evaluated speech recognition in quiet and noise, localization, and perceived benefit.

Results: Second ear performance was similar to 1st ear performance by 6 months postbilateral implantation. Bilateral performance was generally superior to either ear alone; however, participants with shorter 2nd ear length of deafness (<20 years) had more rapid early improvement and better overall outcomes than those with longer 2nd ear length of deafness (>30 years). All participants reported bilateral benefit.

Conclusions: Adult cochlear implant recipients demonstrated benefit from 2nd ear implantation for speech recognition, localization, and perceived communication function. Because performance outcomes were related to length of deafness, shorter time between surgeries may be warranted to reduce negative length-of-deafness effects. Future study may clarify the impact of other variables, such as preimplant hearing aid use, particularly for individuals with longer periods of deafness.

Figures

Figure 1. Theoretical example of HLM curves and components

Examples of two theoretical HLM curves are shown (dotted and dashed lines) with the components indicated. Intercept is the expected performance at a point in time (the centering point) based on the HLM analysis of the group data. Three example intercepts are indicated with open circles along each curve (1, 2, 3 along the dashed line and a, b, c along the dotted line). Expected performance at the earliest point is much higher along the dashed line (1) than the dotted line (a). Linear Slope is the rate of change at a specific point in time (the centering point). That is, the slope of the tangent (gray lines) to the curve at the given time point. The linear slope at the intercept (b) is considerably steeper than the linear slope at the intercept (d). The rate of change is greater at the earlier time point. Curvilinearity is change in the linear component over time. The two example HLM curves differ in curvilinearity. The change over time is minimal for the dashed line and substantial for the dotted line. Each component and each condition has its own significance test that indicates if the parameter estimate is different from 0. For example, it is likely that the linear slope at (b) in Figure 1 would differ from 0 but the linear slope at (d) would not differ from 0. Comparisons of the components between CI conditions were conducted using chisquare tests.

Figure 2. Group mean speech recognition scores at the latest test interval

Group mean speech recognition scores in percent correct (panel A) and dB signal-to-noise ratio (SNR; panel B) at the latest test interval for the three cochlear implant conditions. Note that lower SNR scores indicate better performance. Scores are represented as white bars for the first implanted ear (CI1), gray bars for the second implanted ear (CI2) and black bars for bilateral cochlear implants. Error bars are one standard error. Significant differences are indicated with asterisk(s): *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 3. Group mean results over time

Group mean results over time are indicated for the three cochlear implant (CI) conditions by test measure The squares, diamonds and triangles represent group means at each test interval for the first CI (CI1), the second CI (CI2) and the bilateral conditions respectively . Error bars are one standard deviation. Significant differences are indicated in Table 4.

Figure 4. Scatter plots and correlations for speech recognition measures and cochlear implant conditions

Scatter plots and correlations for each speech recognition measure between second implanted ear (CI2) length of deafness and latest test interval scores for the three cochlear implant conditions: first implanted ear (CI1) in the first column, second implanted ear (CI2) in the second column, and bilateral cochlear implants in the third column. Correlations are indicated on each plot and significance indicated with asterisks (**p < 0.01; ***p < 0.001).

Figure 5. Group mean results over time plotted by length of deafness group

Group mean results over time for the three cochlear implant (CI) conditions are plotted separately for participants in the longer and shorter second implanted ear (CI2) length of deafness (LOD) groups. The longer CI2 LOD group is indicated with gray lines and symbols and includes participants with CI2 LOD > 30 years. The shorter CI2 LOD group is indicated with black lines and symbols and includes participants with CI2 LOD

Figure 6. Group mean RMS localization error in degrees

Panel A graphs the group mean RMS localization error in degrees at three test intervals (pre-bilateral in white, 6 months in gray and 12 months in black) for the first implanted ear (CI1), the second implanted ear (CI2) and bilateral cochlear implants. Panel B graphs the group mean RMS localization error in degrees at the 12-month interval for the longer and shorter second implanted ear (CI2) length of deafness (LOD) groups. Scores are represented as white bars for CI1, gray bars for CI2 and black bars for bilateral cochlear implants. Error bars are one standard error. Significant differences are indicated with asterisks (*p < 0.05; **p < 0.01; ***p < 0.001).

Figure 7. Group mean ratings for the Speech, Spatial and Qualities of Hearing scale

Group mean ratings are plotted over time for the three domains of the Speech, Spatial and Qualities of Hearing scale (Speech, light gray diamonds; Spatial, medium gray squares; Quality, black diamonds). Error bars are one standard error. Significant changes from pre-bilateral are indicated with asterisks (**p < 0.01; ***p < 0.001) and from the 1-month interval with plus signs (+p < 0.05; ++p < 0.01). There were no significant differences between the 3–6 month and 9–12 month periods for any domain.