Luo Xin, Wu Ching-Chih
Department of Speech, Language, and Hearing Sciences, Purdue University, 715 Clinic Dr., West Lafayette, IN, 47907, USA.
Department of Speech and Hearing Science, Arizona State University, Coor Hall, 975 S. Myrtle Av., P.O. Box 870102, Tempe, AZ, 85287, USA.
J Assoc Res Otolaryngol. 2016 Dec;17(6):609-619. doi: 10.1007/s10162-016-0582-8. Epub 2016 Aug 25.
In cochlear implants (CIs), standard partial tripolar (pTP) mode reduces current spread by returning a fraction of the current to two adjacent flanking electrodes within the cochlea. Symmetric electrode spanning (i.e., separating both the apical and basal return electrodes from the main electrode by one electrode) has been shown to increase the pitch of pTP stimuli, when the ratio of intracochlear return current was fixed. To explain the pitch increase caused by symmetric spanning in pTP mode, this study measured the electrical potentials of both standard and symmetrically spanned pTP stimuli on a main electrode EL8 in five CI ears using electrical field imaging (EFI). In addition, the spatial profiles of evoked compound action potentials (ECAP) and the psychophysical forward masking (PFM) patterns were also measured for both stimuli. The EFI, ECAP, and PFM patterns of a given stimulus differed in shape details, reflecting the different levels of auditory processing and different ratios of intracochlear return current across the measurement methods. Compared to the standard pTP stimuli, the symmetrically spanned pTP stimuli significantly reduced the areas under the curves of the normalized EFI and PFM patterns, without shifting the pattern peaks and centroids (both around EL8). The more focused excitation patterns with symmetric spanning may have caused the previously reported pitch increase, due to an interaction between pitch and timbre perception. Being able to reduce the spread of excitation, pTP mode symmetric spanning is a promising stimulation strategy that may further increase spectral resolution and frequency selectivity with CIs.
在人工耳蜗（CI）中，标准部分三极（pTP）模式通过将一部分电流返回耳蜗内两个相邻的侧翼电极来减少电流扩散。当耳蜗内返回电流的比例固定时，对称电极跨距（即从主电极将顶端和基底返回电极都隔开一个电极）已被证明会增加pTP刺激的音调。为了解释pTP模式下对称跨距引起的音调增加，本研究使用电场成像（EFI）测量了5例CI耳中主电极EL8上标准和对称跨距pTP刺激的电势。此外，还测量了两种刺激的诱发复合动作电位（ECAP）的空间分布和心理物理学前向掩蔽（PFM）模式。给定刺激的EFI、ECAP和PFM模式在形状细节上有所不同，反映了不同测量方法下听觉处理的不同水平和耳蜗内返回电流的不同比例。与标准pTP刺激相比，对称跨距的pTP刺激显著减小了归一化EFI和PFM模式曲线下的面积，而没有移动模式峰值和质心（均在EL8周围）。由于音高和音色感知之间的相互作用，对称跨距下更集中的兴奋模式可能导致了先前报道的音调增加。pTP模式对称跨距能够减少兴奋扩散，是一种很有前景的刺激策略，可能会进一步提高人工耳蜗的频谱分辨率和频率选择性。
