Department of Hearing and Speech Sciences, University of Maryland, College Park, MD, 20742, USA.
National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, MD, 20889, USA.
J Assoc Res Otolaryngol. 2019 Apr;20(2):187-203. doi: 10.1007/s10162-018-00707-x. Epub 2019 Jan 8.
By allowing bilateral access to sound, bilateral cochlear implants (BI-CIs) or unilateral CIs for individuals with single-sided deafness (SSD; i.e., normal or near-normal hearing in one ear) can improve sound localization and speech understanding in noise. Spatial hearing in the horizontal plane is primarily conveyed by interaural time and level differences computed from neurons in the superior olivary complex that receive frequency-matched inputs. Because BI-CIs and SSD-CIs do not necessarily convey frequency-matched information, it is critical to understand how to align the inputs to CI users. Previous studies show that interaural pitch discrimination for SSD-CI listeners is highly susceptible to contextual biases, questioning its utility for establishing interaural frequency alignment. Here, we replicate this finding for SSD-CI listeners and show that these biases also extend to BI-CI listeners. To assess the testing-range bias, three ranges of comparison electrodes (BI-CI) or pure-tone frequencies (SSD-CI) were tested: full range, apical/lower half, or basal/upper half. To assess the reference bias, the reference electrode was either held fixed throughout a testing block or randomly chosen from three electrodes (basal end, middle, or apical end of the array). Results showed no effect of reference electrode randomization, but a large testing range bias; changing the center of the testing-range shifted the pitch match by an average 63 % (BI-CI) or 43 % (SSD-CI) of the change magnitude. This bias diminished pitch-match accuracy, with a change in reference electrode shifting the pitch match only an average 34 % (BI-CI) or 40 % (SSD-CI) of the expected amount. Because these effects extended to the relatively more symmetric BI-CI listeners, the results suggest that the bias cannot be attributed to interaural asymmetry. Unless the range effect can be minimized or accounted for, a pitch-discrimination task will produce interaural place-of-stimulation estimates that are highly influenced by the conditions tested, rather than reflecting a true interaural place-pitch comparison.
通过允许双侧声音接入，双侧人工耳蜗植入物（BI-CI）或单侧人工耳蜗植入物（用于单耳聋患者，即一只耳朵的听力正常或接近正常）可以改善单侧聋患者的声源定位和噪声下言语理解。水平面上的空间听觉主要通过从中耳上橄榄复合体接收频率匹配输入的神经元计算出的耳间时间和水平差异来传递。由于 BI-CI 和 SSD-CI 不一定传递频率匹配的信息，因此了解如何将输入与 CI 用户对齐至关重要。先前的研究表明，单侧聋患者的耳间音高辨别能力极易受到上下文偏差的影响，这质疑了其用于建立耳间频率对齐的效用。在这里，我们复制了单侧聋患者的这一发现，并表明这些偏差也扩展到了双侧聋患者。为了评估测试范围偏差，测试了三个比较电极（双侧聋患者）或纯音频率（单侧聋患者）的范围：全范围、顶部/下部一半或底部/上部一半。为了评估参考电极偏差，参考电极要么在整个测试块中保持固定，要么从三个电极（阵列的底部、中间或顶部）中随机选择。结果显示，参考电极随机化没有效果，但测试范围偏差很大；改变测试范围的中心会使音高匹配平均偏移 63%（双侧聋患者）或 43%（单侧聋患者）的变化幅度。这种偏差降低了音高匹配的准确性，改变参考电极仅使音高匹配平均偏移预期值的 34%（双侧聋患者）或 40%（单侧聋患者）。由于这些效果扩展到相对更对称的双侧聋患者，因此结果表明该偏差不能归因于耳间不对称。除非可以最小化或考虑到范围效应，否则音高辨别任务将产生受测试条件强烈影响的耳间刺激位置估计，而不是反映真实的耳间音高比较。
