Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington, USA.
Advanced Bionics Corporation, Valencia, California, USA.
Ear Hear. 2018 Nov/Dec;39(6):1136-1145. doi: 10.1097/AUD.0000000000000566.
The standard, monopolar (MP) electrode configuration used in commercially available cochlear implants (CI) creates a broad electrical field, which can lead to unwanted channel interactions. Use of more focused configurations, such as tripolar and phased array, has led to mixed results for improving speech understanding. The purpose of the present study was to assess the efficacy of a physiologically inspired configuration called dynamic focusing, using focused tripolar stimulation at low levels and less focused stimulation at high levels. Dynamic focusing may better mimic cochlear excitation patterns in normal acoustic hearing, while reducing the current levels necessary to achieve sufficient loudness at high levels.
Twenty postlingually deafened adult CI users participated in the study. Speech perception was assessed in quiet and in a four-talker babble background noise. Speech stimuli were closed-set spondees in noise, and medial vowels at 50 and 60 dB SPL in quiet and in noise. The signal to noise ratio was adjusted individually such that performance was between 40 and 60% correct with the MP strategy. Subjects were fitted with three experimental strategies matched for pulse duration, pulse rate, filter settings, and loudness on a channel-by-channel basis. The strategies included 14 channels programmed in MP, fixed partial tripolar (σ = 0.8), and dynamic partial tripolar (σ at 0.8 at threshold and 0.5 at the most comfortable level). Fifteen minutes of listening experience was provided with each strategy before testing. Sound quality ratings were also obtained.
Speech perception performance for vowel identification in quiet at 50 and 60 dB SPL and for spondees in noise was similar for the three tested strategies. However, performance on vowel identification in noise was significantly better for listeners using the dynamic focusing strategy. Sound quality ratings were similar for the three strategies. Some subjects obtained more benefit than others, with some individual differences explained by the relation between loudness growth and the rate of change from focused to broader stimulation.
These initial results suggest that further exploration of dynamic focusing is warranted. Specifically, optimizing such strategies on an individual basis may lead to improvements in speech perception for more adult listeners and improve how CIs are tailored. Some listeners may also need a longer period of time to acclimate to a new program.
商业上可用的人工耳蜗（CI）中使用的标准单极（MP）电极配置会产生广泛的电场，这可能导致不需要的通道相互作用。使用更集中的配置，如三极和相控阵，可以改善语音理解，但结果不一。本研究的目的是评估一种名为动态聚焦的受生理启发的配置的效果，该配置在低水平使用集中的三极刺激，在高水平使用不那么集中的刺激。动态聚焦可能更好地模拟正常声学听力中的耳蜗激发模式，同时降低在高水平实现足够响度所需的电流水平。
20 名后天聋的成人 CI 用户参加了这项研究。在安静和四人闲聊背景噪声下评估语音感知。语音刺激为噪声中的闭合音节、50 和 60dB SPL 下安静和噪声中的中元音。根据个体情况调整信号噪声比，使 MP 策略的表现在 40%至 60%之间。根据脉冲持续时间、脉冲速率、滤波器设置和通道级别的响度，对三个实验策略进行匹配。这些策略包括在 MP 中编程的 14 个通道、固定部分三极（σ=0.8）和动态部分三极（σ 在阈值处为 0.8，在最舒适水平处为 0.5）。在测试前，每位受试者分别体验 15 分钟的各种策略。还获得了音质评级。
在 50 和 60dB SPL 的安静环境下的元音识别和噪声中的短句识别方面，三种测试策略的语音感知性能相似。然而，在噪声中识别元音方面，使用动态聚焦策略的听众表现明显更好。三种策略的音质评级相似。一些受试者比其他人受益更多，一些个体差异可以通过响度增长与从集中刺激到更广泛刺激的变化率之间的关系来解释。
这些初步结果表明，进一步探索动态聚焦是合理的。具体来说，在个体基础上优化此类策略可能会提高更多成年听众的语音感知能力，并改善 CI 的适配。一些听众可能还需要更长的时间来适应新程序。
