Institute of Medical Science, University of Toronto, Canada.
Ear Hear. 2010 Aug;31(4):441-56. doi: 10.1097/AUD.0b013e3181d4f228.
Interaural level differences (ILD) and interaural timing differences (ITD) are important cues for locating sounds in space. Adult bilateral cochlear implant (CI) users use ILDs more effectively than ITDs. Few studies investigated the ability of children who use bilateral CIs to make use of these binaural cues. Our working hypothesis was that children using bilateral CIs are able to perceive changes in ITDs and ILDs similar to their normal-hearing (NH) peers.
Participants were two groups of children; 19 bilateral implant users (CI) and nine NH children. The children in the CI group had received a second CI after 4.9 +/- 2.8 yrs of unilateral use. Children performed a four alternative forced-choice lateralization task in which they were asked to describe stimuli as coming from the left side, right side, middle of the head, or from both sides simultaneously. Stimuli were 500 msec trains of electrical pulses delivered to apical electrode no. 18 (CI group) or clicks (NH group) presented 11 times per second with either ITDs (0, 400, 1000, or 2000 microsec delay between sides) or level differences (0, 10, or 20 Current Units (CI group) or 0, 10, or 20 dB (NH group) difference between sides). ITDs were presented using current levels that were balanced using left and right electrically evoked brain stem responses. Stimulus levels evoking response amplitudes that were most similar were used.
Responses from children in the CI group changed significantly with changes in ILD of bilateral stimuli, but not with changes in ITD. Responses from children in the CI group were significantly different from those in the NH group in three ways. Children in the CI group perceived bilaterally presented electrical pulses: (1) to come from the second implanted side more often than the first, (2) to rarely come from the middle, and (3) to come from both sides of the head simultaneously. Perceived changes in lateralization with ILD changes were correlated with differences in amplitudes of electrically evoked brain stem responses by the left versus right CI.
The results of this study illustrate that children who use bilateral CIs can lateralize stimuli on the basis of level cues, but have difficulty interpreting interimplant timing differences. Perceived lateralization of bilaterally presented stimuli to the second implanted side in many of the stimulus conditions may relate to the use of different device generations between sides. Further differences from normal lateralization responses could be due to abnormal binaural processing, possibly resulting from a period of unilateral hearing before the provision of a second implant or due to insufficiently matched interimplant stimuli. It may be possible to use objective measures such as electrically evoked auditory brain stem responses wave eV amplitudes to provide balanced levels of bilateral stimulation in children who have had no binaural hearing experience.
耳间水平差（ILD）和耳间时间差（ITD）是用于定位空间中声音的重要线索。双侧人工耳蜗植入（CI）使用者比 ITD 更有效地使用 ILD。很少有研究调查使用双侧 CI 的儿童利用这些双耳线索的能力。我们的工作假设是，使用双侧 CI 的儿童能够感知 ITD 和 ILD 的变化，类似于他们的正常听力（NH）同龄人。
参与者是两组儿童；19 名双侧植入物使用者（CI）和 9 名 NH 儿童。CI 组中的儿童在单侧使用 4.9 +/- 2.8 年后接受了第二次 CI。儿童进行了四项替代强制选择侧化任务，要求他们描述刺激是来自左侧、右侧、头部中间还是同时来自两侧。刺激物是电脉冲的 500 毫秒长的脉冲串，以 CI 组中的 18 号尖端电极（CI 组）或 NH 组中的点击（CI 组）呈现，每秒呈现 11 次，具有 ITD（两侧之间的 0、400、1000 或 2000 微秒延迟）或水平差异（0、10 或 20 电流单位（CI 组）或 0、10 或 20dB（NH 组）差异）。使用左右电诱发脑干反应平衡的电流水平呈现 ITD。使用引发响应幅度最相似的刺激水平。
CI 组儿童的反应随着双侧刺激的 ILD 变化而显著变化，但随着 ITD 的变化而没有变化。CI 组儿童的反应与 NH 组儿童的反应有三个不同之处。CI 组儿童感知双侧呈现的电脉冲：（1）来自第二个植入侧的次数多于第一个，（2）很少来自中间，（3）同时来自头部两侧。随着 ILD 变化感知到的侧化变化与左右 CI 的电诱发脑干反应幅度差异相关。
本研究的结果表明，使用双侧 CI 的儿童可以根据水平线索对刺激进行侧化，但难以解释植入物之间的时间差异。在许多刺激条件下，双侧呈现的刺激对第二个植入侧的感知侧化可能与两侧之间使用不同的设备代际有关。与正常侧化反应的进一步差异可能是由于异常的双耳处理，可能是由于在提供第二个植入物之前单侧听力的一段时间，或者是由于双侧刺激的不匹配。可以使用客观测量，如电诱发听觉脑干反应波 eV 幅度，为没有双耳听力经验的儿童提供双侧刺激的平衡水平。
