Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, England.
Department of Otolaryngology, University of California at Irvine, Irvine, CA, USA.
J Assoc Res Otolaryngol. 2024 Apr;25(2):201-213. doi: 10.1007/s10162-024-00937-2. Epub 2024 Mar 8.
Attempts to use current-focussing strategies with cochlear implants (CI) to reduce neural spread-of-excitation have met with only mixed success in human studies, in contrast to promising results in animal studies. Although this discrepancy could stem from between-species anatomical and aetiological differences, the masking experiments used in human studies may be insufficiently sensitive to differences in excitation-pattern width.
We used an interleaved-masking method to measure psychophysical excitation patterns in seven participants with four masker stimulation configurations: monopolar (MP), partial tripolar (pTP), a wider partial tripolar (pTP + 2), and, importantly, a condition (RP + 2) designed to produce a broader excitation pattern than MP. The probe was always in partial-tripolar configuration.
We found a significant effect of stimulation configuration on both the amount of on-site masking (mask and probe on same electrode; an indirect indicator of sharpness) and the difference between off-site and on-site masking. Differences were driven solely by RP + 2 producing a broader excitation pattern than the other configurations, whereas monopolar and the two current-focussing configurations did not statistically differ from each other.
A method that is sensitive enough to reveal a modest broadening in RP + 2 showed no evidence for sharpening with focussed stimulation. We also showed that although voltage recordings from the implant accurately predicted a broadening of the psychophysical excitation patterns with RP + 2, they wrongly predicted a strong sharpening with pTP + 2. We additionally argue, based on our recent research, that the interleaved-masking method can usefully be applied to non-human species and objective measures of CI excitation patterns.
试图在使用耳蜗植入物（CI）时采用目前的聚焦策略来减少神经兴奋扩散，在人体研究中仅取得了混合成功，而在动物研究中则取得了有希望的结果。尽管这种差异可能源于物种间的解剖学和病因学差异，但人体研究中使用的掩蔽实验可能对兴奋模式宽度的差异不够敏感。
我们使用交错掩蔽方法在七名参与者中测量了心理物理兴奋模式，有四种掩蔽器刺激配置：单极（MP）、部分三极（pTP）、较宽的部分三极（pTP+2），以及重要的是一种条件（RP+2），其设计目的是产生比 MP 更宽的兴奋模式。探针始终处于部分三极配置。
我们发现刺激配置对现场掩蔽（掩蔽器和探针在同一电极上；尖锐度的间接指标）和现场掩蔽与现场掩蔽之间的差异都有显著影响。差异仅由 RP+2 产生的比其他配置更宽的兴奋模式驱动，而单极和两种电流聚焦配置彼此之间没有统计学差异。
一种足够灵敏的方法可以揭示 RP+2 适度增宽，但没有证据表明聚焦刺激会变锋利。我们还表明，尽管来自植入物的电压记录准确预测了 RP+2 时心理物理兴奋模式的变宽，但它们错误地预测了 pTP+2 时强烈的变锋利。我们还基于我们最近的研究提出，交错掩蔽方法可有效地应用于非人类物种和 CI 兴奋模式的客观测量。
