van Hoesel Richard J M, Tyler Richard S
CRC for Cochlear Implant and Hearing Aid Innovation, Melbourne, Victoria, Australia.
J Acoust Soc Am. 2003 Mar;113(3):1617-30. doi: 10.1121/1.1539520.
Five bilateral cochlear implant users were tested for their localization abilities and speech understanding in noise, for both monaural and binaural listening conditions. They also participated in lateralization tasks to assess the impact of variations in interaural time delays (ITDs) and interaural level differences (ILDs) for electrical pulse trains under direct computer control. The localization task used pink noise bursts presented from an eight-loudspeaker array spanning an arc of approximately 108 degrees in front of the listeners at ear level (0-degree elevation). Subjects showed large benefits from bilateral device use compared to either side alone. Typical root-mean-square (rms) averaged errors across all eight loudspeakers in the array were about 10 degrees for bilateral device use and ranged from 20 degrees to 60 degrees using either ear alone. Speech reception thresholds (SRTs) were measured for sentences presented from directly in front of the listeners (0 degrees) in spectrally matching speech-weighted noise at either 0 degrees, +90 degrees or -90 degrees for four subjects out of five tested who could perform the task. For noise to either side, bilateral device use showed a substantial benefit over unilateral device use when noise was ipsilateral to the unilateral device. This was primarily because of monaural head-shadow effects, which resulted in robust SRT improvements (P<0.001) of about 4 to 5 dB when ipsilateral and contralateral noise positions were compared. The additional benefit of using both ears compared to the shadowed ear (i.e., binaural unmasking) was only 1 or 2 dB and less robust (P = 0.04). Results from the lateralization studies showed consistently good sensitivity to ILDs; better than the smallest level adjustment available in the implants (0.17 dB) for some subjects. Sensitivity to ITDs was moderate on the other hand, typically of the order of 100 micros. ITD sensitivity deteriorated rapidly when stimulation rates for unmodulated pulse-trains increased above a few hundred Hz but at 800 pps showed sensitivity comparable to 50-pps pulse-trains when a 50-Hz modulation was applied. In our opinion, these results clearly demonstrate important benefits are available from bilateral implantation, both for localizing sounds (in quiet) and for listening in noise when signal and noise sources are spatially separated. The data do indicate, however, that effects of interaural timing cues are weaker than those from interaural level cues and according to our psychophysical findings rely on the availability of low-rate information below a few hundred Hz.
对5名双侧人工耳蜗使用者进行了测试，以评估他们在单耳和双耳聆听条件下的声音定位能力以及噪声环境下的言语理解能力。他们还参与了侧向化任务，以评估在计算机直接控制下，电脉冲序列的双耳时间延迟（ITD）和双耳声级差（ILD）变化的影响。定位任务使用粉红色噪声脉冲，由一个八扬声器阵列发出，该阵列在听众耳部高度（仰角0度）前方形成一个约108度的弧形。与单独使用任一侧设备相比，受试者从双侧设备使用中获得了显著益处。阵列中所有八个扬声器的典型均方根（rms）平均误差，双侧设备使用时约为10度，单独使用任一只耳朵时则在20度至60度之间。对五名接受测试且能够完成任务的受试者中的四名，测量了在0度、+90度或 -90度的频谱匹配言语加权噪声中，从听众正前方（0度）呈现的句子的言语接受阈值（SRT）。对于任一侧的噪声，当噪声与单侧设备同侧时，双侧设备使用比单侧设备使用显示出显著优势。这主要是由于单耳头影效应，当比较同侧和对侧噪声位置时，导致SRT显著提高（P<0.001）约4至5 dB。与被遮蔽的耳朵相比（即双耳掩蔽），使用双耳的额外益处仅为1或2 dB，且不太显著（P = 0.04）。侧向化研究结果始终显示对ILD具有良好的敏感性；对于某些受试者，优于植入设备中可用的最小声级调整（0.17 dB）。另一方面，对ITD的敏感性适中，通常约为100微秒。当未调制脉冲序列的刺激速率增加到几百赫兹以上时，ITD敏感性迅速下降，但在800pps时，当应用50Hz调制时，显示出与50pps脉冲序列相当的敏感性。我们认为，这些结果清楚地表明，双侧植入对于（在安静环境中）声音定位以及信号和噪声源在空间上分离时的噪声聆听都有重要益处。然而，数据确实表明，双耳时间线索的影响比双耳声级线索的影响弱，并且根据我们的心理物理学研究结果，依赖于低于几百赫兹的低速率信息。
