Yang-Soo Yoon

Objectives: This study investigated whether a spectral mismatch across ears influences the benefit of redundancy, squelch, and head shadow differently in speech perception using acoustic simulation of bilateral cochlear implant (CI) processing. Design: Ten normal-hearing subjects participated in the study, and acoustic simulations of CIs were used to test these subjects. Sentence recognition, presented unilaterally and bilaterally, was measured at +5 dB and +10 dB signal-to-noise ratios (SNRs) with bilaterally matched and mismatched conditions. Unilateral and bilateral CIs were simulated using 8-channel sine wave vocoders. Binaural spectral mismatch was introduced by changing the relative simulated insertion depths across ears. Subjects were tested while listening with headphones; head-related transfer functions were applied before the vocoder processing to preserve natural interaural level and time differences. Results: For both SNRs, greater and more consistent binaural benefit of squelch and redundancy occurred for the matched condition whereas binaural interference of squelch and redundancy occurred for the mismatched condition. However, significant binaural benefit of head shadow existed irrespective of spectral mismatches and SNRs. Conclusions: The results suggest that bilateral spectral mismatch may have a negative impact on the binaural benefit of squelch and redundancy for bilateral CI users. The results also suggest that clinical mapping should be carefully administrated for bilateral CI users to minimize the difference in spectral patterns between the two CIs.

Objective To compare the speech perception benefit, provided by a contralateral hearing aid (HA) or a second cochlear implant (CI). Study Design Repeated measures. Patients A total of 25 adult subjects participated in the study, including 12 bilateral (10 female and 2 male patients) and 13 bimodal (6 female and 7 male subjects) users. All bilateral users were sequentially implanted. The bimodal users were separated into a poor group (n = 5, aided pure-tone average (PTA) of 55 dB HL or greater at audiometric frequencies of 1 kHz or lesser) and a good group (n = 8, aided PTA < 55 dB HL). Main Outcome Measures Consonant, vowel, and sentence recognition was measured in quiet and noise at +5 dB and +10 dB signal-to-noise ratios (SNRs). Speech recognition performance was evaluated under three listening conditions: CI alone, HA alone, and CI+HA for bimodal users; first CI alone, second CI alone, and first CI + second CI for bilateral users when speech and noise were presented from the front. Results There was no significant difference in the binaural benefit between the good bimodal and bilateral groups in vowel and sentence recognition. However, the binaural benefit is significantly better in the bilateral group than in the poor bimodal group for all 3 speech measures. Conclusion These results suggest that the aided pure-tone average at audiometric frequencies of 1 kHz or lesser may serve as one of the clinical criteria for the recommendation of whether bimodal patients should consider a second cochlear implant to maximize their binaural listening ability.

Purpose: Although poorer understanding of speech in noise by listeners who are hearing-impaired (HI) is known not to be directly related to audiometric hearing threshold, HT (f), grouping HI listeners with HT (f) is widely practiced. In this article, the relationship between consonant recognition and HT (f) is considered over a range of signal-to-noise ratios (SNRs). Method: Confusion matrices (CMs) from 25 HI ears were generated in response to 16 consonant-vowel syllables presented at 6 different SNRs. Individual differences scaling (INDSCAL) was applied to both feature-based matrices and CMs in order to evaluate the relationship between HT (f) and consonant recognition among HI listeners. Results: The results showed no predictive relationship between the percent error scores ( Pe ) and HT (f) across SNRs. The multiple regression models showed that the HT (f) accounted for 39% of the total variance of the slopes of the Pe . Feature-based INDSCAL analysis showed consistent grouping of listeners across SNRs, but not in terms of HT (f). Systematic relationship between measures was also not defined by CM-based INDSCAL analysis across SNRs. Conclusions: HT (f) did not account for the majority of the variance (39%) in consonant recognition in noise when the complete body of the CM was considered.

Purpose: In this study, the authors aimed to identify speech information processed by a hearing aid (HA) that is additive to information processed by a cochlear implant (CI) as a function of signal-to-noise ratio (SNR). Method: Speech recognition was measured with CI alone, HA alone, and CI + HA. Ten participants were separated into 2 groups; good (aided pure-tone average [PTA] < 55 dB) and poor (aided PTA ≥ 55 dB) at audiometric frequencies ≤ 1 kHz in HA. Results: Results showed that the good-aided PTA group derived a clear bimodal benefit (performance difference between CI + HA and CI alone) for vowel and sentence recognition in noise, whereas the poor-aided PTA group received little benefit across speech tests and SNRs. Results also showed that a better aided PTA helped in processing cues embedded in both low and high frequencies; none of these cues was significantly perceived by the poor-aided PTA group. Conclusions: The aided PTA is an important indicator for bimodal advantage in speech perception. The lack of bimodal benefits in the poor group may be attributed to the nonoptimal HA fitting. Bimodal listening provides a synergistic effect for cues in both low- and high-frequency components in speech.

The present study investigated the effects of binaural spectral mismatch on binaural benefits in the context of bilateral cochlear implants using acoustic simulations. Binaural spectral mismatch was systematically manipulated by simulating changes in the relative insertion depths across ears. Sentence recognition, presented unilaterally and bilaterally, were measured in normal-hearing listeners in quiet and noise at +5 dB signal-to-noise ratio. Significant binaural benefits were observed when the interaural difference in insertion depth was 1 mm or less. This result suggests a dependence of the binaural benefit on redundant speech information, rather than on similarity in performance across ears.

Objective: The full benefit of bilateral cochlear implants may depend on the unilateral performance with each device, the speech materials, processing ability of the user, and/or the listening environment. In this study, bilateral and unilateral speech performances were evaluated in terms of recognition of phonemes and sentences presented in quiet or in noise. Design: Speech recognition was measured for unilateral left, unilateral right, and bilateral listening conditions; speech and noise were presented at 0° azimuth. The ‘binaural benefit’ was defined as the difference between bilateral performance and unilateral performance with the better ear. Study sample: Nine adults with bilateral cochlear implants participated. Results: On average, results showed a greater binaural benefit in noise than in quiet for all speech tests. More importantly, the binaural benefit was greater when unilateral performance was similar across ears. As the difference in unilateral performance between ears increased, the binaural advantage decreased; this functional relationship was observed across the different speech materials and noise levels even though there was substantial intra- and inter-subject variability. Conclusions: The results indicate that subjects who show symmetry in speech recognition performance between implanted ears in general show a large binaural benefit. Sumario Objetivo: Se estudiaron los datos audiológicos de investigación epidemiológica basada en una población de adultos mayores. Se buscaron diagnósticos específicos de alteraciones otológicas y audiológicas que pueden ocasionar hipoacusia. Diseño: Estudio retrospectivo de registros. Muestra: Se estudiaron tres cohortes etáreas, 474 individuos de 70 a 75 años (“jóvenes) y 252 individuos de 85 años o mayores (“viejos”). Se utilizaron las audiometrías de tonos puros y de lenguaje. Se incluyeron los datos de sus expedientes médicos. Resultados: Se diagnosticó hipoacusia conductiva en 6.1% del grupo de “jóvenes” y un 10.3% de los “viejos”. Se establecieron diagnósticos especfícos (otitis media crónica y otoesclerosis) en cerca de la mitad de los casos. Se diagnosticó hipoacusia sensorineural no relacionada con la edad ni inducida por ruido en 3.4 y 5.2% de los casos. El 0.4% del grupo de “jóvenes” y el 10% del grupo de “viejos” presentaban un reconocimiento del lenguaje severamente afectado, posiblemente relacionado con neuropatía auditiva por edad. El 3.2% de las personas de 85 años de edad presentaban sordera funcional bilateral, pero ésta no se presentó en el grupo de 70–75 años. Conclusiones: La incidencia de neuropatíaa auditiva probablemente relacionada con la edad aumenta considerablemente de los 70–75 años a los 85. Existen marcadas diferencias en cuando a hipoacusia que afecta severamente la comunicación entre los grupos de “jóvenes” y “viejos” en la población estudiada.

While considerable evidence suggests that bilateral cochlear implant (CI) users’ sound localization abilities rely primarily on interaural level difference (ILD) cues, and only secondarily, if at all, on interaural time difference (ITD) cues, this evidence has largely been indirect. This study used head-related transfer functions (HRTFs) to independently manipulate ITD and ILD cues and directly measure their contribution to bilateral CI users’ localization abilities. The results revealed a strong reliance on ILD cues, but some CI users also made use of ITD cues. The results also suggest a complex interaction between ITD and ILD cues.