Department of Speech and Hearing Science, Arizona State University, Tempe, AZ.
Ear Hear. 2018 Nov/Dec;39(6):1224-1231. doi: 10.1097/AUD.0000000000000581.
We report on the ability of patients fit with bilateral cochlear implants (CIs) to distinguish the front-back location of sound sources both with and without head movements. At issue was (i) whether CI patients are more prone to front-back confusions than normal hearing listeners for wideband, high-frequency stimuli; and (ii) if CI patients can utilize dynamic binaural difference cues, in tandem with their own head rotation, to resolve these front-back confusions. Front-back confusions offer a binary metric to gain insight into CI patients' ability to localize sound sources under dynamic conditions not generally measured in laboratory settings where both the sound source and patient are static.
Three-second duration Gaussian noise samples were bandpass filtered to 2 to 8 kHz and presented from one of six loudspeaker locations located 60° apart, surrounding the listener. Perceived sound source localization for seven listeners bilaterally implanted with CIs, was tested under conditions where the patient faced forward and did not move their head and under conditions where they were encouraged to moderately rotate their head. The same conditions were repeated for 5 of the patients with one implant turned off (the implant at the better ear remained on). A control group of normal hearing listeners was also tested for a baseline of comparison.
All seven CI patients demonstrated a high rate of front-back confusions when their head was stationary (41.9%). The proportion of front-back confusions was reduced to 6.7% when these patients were allowed to rotate their head within a range of approximately ± 30°. When only one implant was turned on, listeners' localization acuity suffered greatly. In these conditions, head movement or the lack thereof made little difference to listeners' performance.
Bilateral implantation can offer CI listeners the ability to track dynamic auditory spatial difference cues and compare these changes to changes in their own head position, resulting in a reduced rate of front-back confusions. This suggests that, for these patients, estimates of auditory acuity based solely on static laboratory settings may underestimate their real-world localization abilities.
我们报告双侧人工耳蜗植入（CI）患者辨别声源前后位置的能力，包括有头动和无头动两种情况。主要关注两个问题：（i）与正常听力者相比，CI 患者在听到宽带高频刺激时是否更容易出现前后混淆；（ii）如果 CI 患者可以利用自身头部旋转与动态双耳差异线索相结合来解决这些前后混淆。前后混淆提供了一个二进制指标，可以深入了解 CI 患者在实验室环境中通常无法测量的动态条件下定位声源的能力，在实验室环境中，声源和患者都是静态的。
持续时长为 3 秒的高斯噪声样本经带通滤波至 2 至 8 kHz，并从 60°间隔的六个扬声器位置之一呈现。七位双侧 CI 植入患者在以下两种情况下测试感知声源定位：一种是患者面朝前方且不移动头部，另一种是鼓励患者适度旋转头部。对于 5 位患者中的 1 位植入物关闭（较好耳的植入物保持开启）的情况，重复了相同的条件。还对一组正常听力的对照组进行了测试，作为基准进行比较。
当患者头部静止时，所有七位 CI 患者都表现出较高的前后混淆率（41.9%）。当允许患者在大约±30°范围内旋转头部时，前后混淆率降低至 6.7%。当只有一个植入物开启时，听众的定位准确性会大幅下降。在这些情况下，头动或无头动对听众的表现影响不大。
双侧植入可以为 CI 听众提供跟踪动态听觉空间差异线索的能力，并将这些变化与自身头部位置的变化进行比较，从而降低前后混淆的发生率。这表明，对于这些患者，仅基于静态实验室设置的听觉锐度估计可能低估了他们在现实世界中的定位能力。
