Effect of aided hearing in the nonimplanted ear on bimodal hearing

This study was designed to evaluate the binaural effects from bimodal hearing according to the aided hearing threshold in the nonimplanted ear.

Subjects included 17 individuals who continued to use a hearing aid (HA) in the nonimplanted ear for more than 6 months postoperatively. Speech perception and sound localization were tested with unilateral cochlear implantation (CI) and bimodal hearing with and without background noise. Materials were presented at an average of 70 dB sound pressure level from a front loudspeaker in a quiet condition and then with background noise at a signal-to-noise ratio of +10 dB HL. Speech perception scores were based on percent-correct performance of repeating a spoken word under each condition. Sound localization scores were obtained by averaging the sum of angle differences between the active loudspeaker and the loudspeaker indicated by the subject.

Speech perception scores (mean ± SD) of unilateral CI and bimodal hearing were 63.3% ± 17.7% and 73.1% ± 18.5% under the quiet condition (p = 0.029) and 65.5% ± 21.9% and 70.9% ± 23.6% under the noisy condition (p = 0.01), respectively. Angle differences (mean ± SD) of unilateral CI and bimodal hearing were 72.8 ± 27.4 degrees and 84.1 ± 29.9 degrees under the quiet condition (p = 0.052) and 79.3 ± 26.9 degrees and 77.3 ± 22.0 degrees under the noisy condition (p = 0.906), respectively. Patients were divided into two groups according to their aided hearing thresholds: Group 1 (aided hearing threshold ≤50 dB HL; n = 8) and Group 2 (aided hearing threshold >50 dB HL; n = 9). The speech perception scores of bimodal hearing in each group were 85.3% ± 13.3% and 60.8% ± 17.5% (p = 0.023) under the quiet condition and 82.7% ± 9.0% and 59.4% ± 26.8% under the noisy condition (p = 0.052), respectively. For sound localization, the angle differences of bimodal hearing in each group were 54 ± 28.6 degrees and 83.9 ± 11.9 degrees under the quiet condition (p = 0.042) and 63.0 ± 23.5 degrees and 89 ± 22.6 degrees under the noisy condition (p = 0.049), respectively.

Based on the relationship between the aided hearing level and bimodal hearing performance, this current study suggests that bimodal benefits for sound localization and speech perception in noise are significant but only when sound detection is adequate for the hearing aids. Therefore, bimodal hearing could be applied to selective patients with favorable aided hearing levels.