Zhou Ning, Cadmus Matthew, Dong Lixue, Mathews Juliana
Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27858, USA.
J Assoc Res Otolaryngol. 2018 Jun;19(3):317-330. doi: 10.1007/s10162-018-0663-y. Epub 2018 Apr 25.
Prior research has shown that in electrical hearing, cochlear implant (CI) users' speech recognition performance is related in part to their ability to detect temporal modulation (i.e., modulation sensitivity). Previous studies have also shown better speech recognition when selectively stimulating sites with good modulation sensitivity rather than all stimulation sites. Site selection based on channel interaction measures, such as those using imaging or psychophysical estimates of spread of neural excitation, has also been shown to improve speech recognition. This led to the question of whether temporal modulation sensitivity and spatial selectivity of neural excitation are two related variables. In the present study, CI users' modulation sensitivity was compared for sites with relatively broad or narrow neural excitation patterns. This was achieved by measuring temporal modulation detection thresholds (MDTs) at stimulation sites that were significantly different in their sharpness of the psychophysical spatial tuning curves (PTCs) and measuring MDTs at the same sites in monopolar (MP) and bipolar (BP) stimulation modes. Nine postlingually deafened subjects implanted with Cochlear Nucleus® device took part in the study. Results showed a significant correlation between the sharpness of PTCs and MDTs, indicating that modulation detection benefits from a more spatially restricted neural activation pattern. There was a significant interaction between stimulation site and mode. That is, using BP stimulation only improved MDTs at stimulation sites with broad PTCs but had no effect or sometimes a detrimental effect on MDTs at stimulation sites with sharp PTCs. This interaction could suggest that a criterion number of nerve fibers is needed to achieve optimal temporal resolution, and, to achieve optimized speech recognition outcomes, individualized selection of site-specific current focusing strategies may be necessary. These results also suggest that the removal of stimulation sites measured with poor MDTs might improve both temporal and spectral resolution.
先前的研究表明，在电听觉中，人工耳蜗（CI）使用者的言语识别表现部分与其检测时间调制的能力（即调制敏感性）有关。先前的研究还表明，选择性刺激具有良好调制敏感性的部位而非所有刺激部位时，言语识别效果更好。基于通道相互作用测量的部位选择，例如那些使用神经兴奋扩散的成像或心理物理学估计的方法，也已被证明可以改善言语识别。这就引出了一个问题，即神经兴奋的时间调制敏感性和空间选择性是否是两个相关变量。在本研究中，比较了人工耳蜗使用者在神经兴奋模式相对较宽或较窄的部位的调制敏感性。这是通过测量心理物理学空间调谐曲线（PTC）锐度显著不同的刺激部位的时间调制检测阈值（MDT），以及在单极（MP）和双极（BP）刺激模式下在相同部位测量MDT来实现的。九名植入科利耳公司（Cochlear Nucleus®）设备的语后聋受试者参与了该研究。结果显示PTC的锐度与MDT之间存在显著相关性，表明调制检测受益于更具空间限制的神经激活模式。刺激部位和模式之间存在显著交互作用。也就是说，仅使用BP刺激仅改善了PTC较宽的刺激部位的MDT，但对PTC尖锐的刺激部位的MDT没有影响，有时甚至有不利影响。这种交互作用可能表明需要一定数量的神经纤维来实现最佳的时间分辨率，并且为了实现优化的言语识别结果，可能需要针对特定部位的电流聚焦策略进行个性化选择。这些结果还表明，去除MDT测量结果较差的刺激部位可能会改善时间和频谱分辨率。
