Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, A-1040 Vienna, Austria.
J Acoust Soc Am. 2011 Sep;130(3):1515-29. doi: 10.1121/1.3613704.
The envelope shape is important for the perception of interaural time difference (ITD) in the envelope as supported by the improved sensitivity for transposed tones compared to sinusoidally amplitude-modulated (SAM) tones. The present study investigated the effects of specific envelope parameters in nine normal-hearing (NH) and seven cochlear-implant (CI) listeners, using high-rate carriers with 27-Hz trapezoidal modulation. In NH listeners, increasing the off time (the silent interval in each modulation cycle) up to 12 ms, increasing the envelope slope from 6 to 8 dB/ms, and increasing the peak level improved ITD sensitivity. The combined effect of the off time and slope accounts for the gain in sensitivity for transposed tones relative to SAM tones. In CI listeners, increasing the off time up to 20 ms improved sensitivity, but increasing the slope showed no systematic effect. A 27-pulses/s electric pulse train, representing a special case of modulation with infinitely steep slopes and maximum possible off time, yielded considerably higher sensitivity compared to the best condition with trapezoidal modulation. Overall, the results of this study indicate that envelope-ITD sensitivity could be improved by using CI processing schemes that simultaneously increase the off time and the peak level of the signal envelope.
信封形状对于包络中两耳时间差（ITD）的感知很重要，这一点得到了支持，即与正弦幅度调制（SAM）音调相比，转调音调的灵敏度提高。本研究使用具有 27-Hz 梯形调制的高载波率，调查了九名正常听力（NH）和七名人工耳蜗植入（CI）听众的特定包络参数的影响。在 NH 听众中，将休止时间（每个调制周期中的静音间隔）增加到 12 毫秒，将包络斜率从 6 增加到 8 dB/ms，并增加峰值水平，均可提高 ITD 灵敏度。休止时间和斜率的综合效应解释了转调音调相对于 SAM 音调的灵敏度增益。在 CI 听众中，将休止时间增加到 20 毫秒可提高灵敏度，但斜率增加没有系统影响。27 个脉冲/秒的电脉冲序列代表具有无限陡峭斜率和最大可能休止时间的调制的特殊情况，与具有梯形调制的最佳条件相比，灵敏度显著提高。总体而言，本研究的结果表明，通过使用同时增加信号包络的休止时间和峰值水平的 CI 处理方案，可以提高包络-ITD 灵敏度。
