Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom.
J Acoust Soc Am. 2019 Mar;145(3):1389. doi: 10.1121/1.5093623.
This study simulated the effect of unlinked automatic gain control (AGC) and head movement on the output levels and resulting inter-aural level differences (ILDs) produced by bilateral cochlear implant (CI) processors. The angular extent and velocity of the head movements were varied in order to observe the interaction between unlinked AGC and head movement. Static, broadband input ILDs were greatly reduced by the high-ratio, slow-time-constant AGC used. The size of head-movement-induced dynamic ILDs depended more on the velocity and angular extent of the head movement than on the angular position of the source. The profiles of the dynamic, broadband output ILDs were very different from the dynamic, broadband input ILD profiles. Short-duration, high-velocity head movements resulted in dynamic output ILDs that continued to change after head movement had stopped. Analysis of narrowband, single-channel ILDs showed that static output ILDs were reduced across all frequencies, producing low-frequency ILDs of the opposite sign to the high-frequency ILDs. During head movements, low- and high-frequency ILDs also changed with opposite sign. The results showed that the ILDs presented to bilateral CI listeners during head turns were highly distorted by the interaction of the bilateral, unlinked AGC and the level changes induced by head movement.
本研究模拟了非关联自动增益控制（AGC）和头部运动对双侧人工耳蜗（CI）处理器产生的输出水平和由此产生的耳间水平差（ILD）的影响。改变头部运动的角度范围和速度，以观察非关联 AGC 和头部运动之间的相互作用。使用高比率、慢时间常数 AGC，大大降低了静态、宽带输入 ILD。头部运动引起的动态 ILD 的大小更多地取决于头部运动的速度和角度范围，而不是声源的角度位置。动态、宽带输出 ILD 的轮廓与动态、宽带输入 ILD 的轮廓非常不同。短持续时间、高速度的头部运动导致动态输出 ILD 在头部运动停止后继续变化。对窄带、单通道 ILD 的分析表明，所有频率的静态输出 ILD 都降低了，产生了与高频 ILD 相反符号的低频 ILD。在头部运动期间，低频和高频 ILD 也以相反的符号变化。结果表明，在头部转动期间呈现给双侧 CI 聆听者的 ILD 受到双侧非关联 AGC 的相互作用以及头部运动引起的水平变化的高度扭曲。
