Fitzgerald Matthew B, Kan Alan, Goupell Matthew J
1Department of Otolaryngology-Head and Neck Surgery, Stanford University, Palo Alto, California, USA; 2Department of Otolaryngology, New York University School of Medicine, New York, New York, USA; 3Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, USA; and 4Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland, USA.
Ear Hear. 2015 Sep-Oct;36(5):e225-36. doi: 10.1097/AUD.0000000000000174.
To determine whether bilateral loudness balancing during mapping of bilateral cochlear implants (CIs) produces fused, punctate, and centered auditory images that facilitate lateralization with stimulation on single-electrode pairs.
Adopting procedures similar to those that are practiced clinically, direct stimulation was used to obtain most-comfortable levels (C levels) in recipients of bilateral CIs. Three pairs of electrodes, located in the base, middle, and apex of the electrode array, were tested. These electrode pairs were loudness-balanced by playing right-left electrode pairs sequentially. In experiment 1, the authors measured the location, number, and compactness of auditory images in 11 participants in a subjective fusion experiment. In experiment 2, the authors measured the location and number of the auditory images while imposing a range of interaural level differences (ILDs) in 13 participants in a lateralization experiment. Six of these participants repeated the mapping process and lateralization experiment over three separate days to determine the variability in the procedure.
In approximately 80% of instances, bilateral loudness balancing was achieved from relatively small adjustments to the C levels (≤3 clinical current units). More important, however, was the observation that in 4 of 11 participants, simultaneous bilateral stimulation regularly elicited percepts that were not fused into a single auditory object. Across all participants, approximately 23% of percepts were not perceived as fused; this contrasts with the 1 to 2% incidence of diplacusis observed with normal-hearing individuals. In addition to the unfused images, the perceived location was often offset from the physical ILD. On the whole, only 45% of percepts presented with an ILD of 0 clinical current units were perceived as fused and heard in the center of the head. Taken together, these results suggest that distortions to the spatial map remain common in bilateral CI recipients even after careful bilateral loudness balancing.
The primary conclusion from these experiments is that, even after bilateral loudness balancing, bilateral CI recipients still regularly perceive stimuli that are unfused, offset from the assumed zero ILD, or both. Thus, while current clinical mapping procedures for bilateral CIs are sufficient to enable many of the benefits of bilateral hearing, they may not elicit percepts that are thought to be optimal for sound-source location. As a result, in the absence of new developments in signal processing for CIs, new mapping procedures may need to be developed for bilateral CI recipients to maximize the benefits of bilateral hearing.
确定双侧人工耳蜗（CI）图谱绘制过程中的双侧响度平衡是否能产生融合、点状且居中的听觉图像，从而便于通过单电极对刺激进行声源定位。
采用与临床实践类似的程序，对双侧CI植入者进行直接刺激以获取最舒适响度水平（C水平）。测试了位于电极阵列基部、中部和顶部的三对电极。通过依次播放左右电极对来实现这些电极对的响度平衡。在实验1中，作者在一项主观融合实验中测量了11名参与者听觉图像的位置、数量和紧凑程度。在实验2中，作者在一项声源定位实验中对13名参与者施加一系列双耳声级差（ILD），同时测量听觉图像的位置和数量。其中6名参与者在三个不同日期重复了图谱绘制过程和声源定位实验，以确定该程序的可变性。
在大约80%的情况下，通过对C水平进行相对较小的调整（≤3个临床电流单位）即可实现双侧响度平衡。然而更重要的是，观察发现11名参与者中有4人在同时进行双侧刺激时，经常会产生未融合成单个听觉对象的感知。在所有参与者中，约23%的感知未被视为融合；这与正常听力个体中1%至2%的复听发生率形成对比。除了未融合的图像外，感知到的位置往往偏离实际的双耳声级差。总体而言，在双耳声级差为0个临床电流单位的情况下，只有45%的感知被视为融合且在头部中央听到。综合这些结果表明，即使经过仔细的双侧响度平衡，双侧CI植入者的空间图谱仍经常出现失真。
这些实验的主要结论是，即使经过双侧响度平衡，双侧CI植入者仍经常感知到未融合、偏离假定的零双耳声级差或两者皆有的刺激。因此，虽然目前双侧CI的临床图谱绘制程序足以实现双侧听力的许多益处，但它们可能无法引发被认为对声源定位最理想的感知。因此，在CI信号处理没有新进展的情况下，可能需要为双侧CI植入者开发新的图谱绘制程序，以最大限度地发挥双侧听力的益处。
