Department of Physics, Faculty of Science, University of Split, Ruđera Boškovića 33, 21000, Split, Croatia.
Cochlear France SAS, 135 Route de Saint Simon, 31100, Toulouse, France.
J Assoc Res Otolaryngol. 2022 Oct;23(5):665-680. doi: 10.1007/s10162-022-00854-2. Epub 2022 Aug 2.
The stimulation rate in cochlear implant (CI) sound coding, or the "carrier" rate in pulses per second (pps), is known to influence pitch perception, as well as loudness perception and sound quality. Our main objective was to investigate the effects of reduced carrier rate on the loudness and pitch of coded speech samples. We describe two experiments with 16 Nucleus® CI users, where we controlled modulation characteristics and carrier rate using Spectral and Temporal Enhanced Processing (STEP), a novel experimental multichannel sound coder. We used a fixed set of threshold and comfortable stimulation levels for each subject, obtained from clinical MAPs. In the first experiment, we determined equivalence for voice pitch ranking and voice gender categorization between the Advanced Combination Encoder (ACE), a widely used clinical strategy in Nucleus® recipients, and STEP for fundamental frequencies (F0) 120-250 Hz. In the second experiment, loudness was determined as a function of the input amplitude of speech samples for carrier rates of 1000, 500, and 250 pps per channel. Then, using equally loud sound coder programs, we evaluated the effect of carrier rate on voice pitch perception. Although nearly all subjects could categorize voice gender significantly above chance, pitch ranking varied across subjects. Overall, carrier rate did not substantially affect voice pitch ranking or voice gender categorization: as long as the carrier rate was at least twice the fundamental frequency, or when stimulation pulses for the lowest, 250 pps carrier were aligned to F0 peaks. These results indicate that carrier rates as low as 250 pps per channel are sufficient to support functional voice pitch perception for those CI users sensitive to temporal pitch cues; at least when temporal modulations and pulse timings in the coder output are well controlled by novel strategies such as STEP.
刺激率在人工耳蜗（CI）声音编码中，或在每秒脉冲数（pps）中的“载波”率，已知会影响音高感知，以及响度感知和声音质量。我们的主要目标是研究降低载波率对编码语音样本的响度和音高的影响。我们描述了两项实验，共有 16 名 Nucleus® CI 用户参与，其中我们使用 Spectral and Temporal enhanced Processing（STEP）控制调制特征和载波率，这是一种新的实验性多通道声音编码器。我们使用每个受试者从临床 MAPs 获得的固定阈值和舒适刺激水平来控制刺激。在第一个实验中，我们确定了在语音基频（F0）120-250 Hz 下，新型实验性多通道声音编码器 STEP 与 Nucleus®接受者中广泛使用的高级组合编码（ACE）在语音音高排序和语音性别分类方面的等效性。在第二个实验中，我们确定了语音样本的输入幅度与载波率之间的关系，载波率为 1000、500 和 250 pps/通道。然后，使用相同响度的声音编码器程序，我们评估了载波率对语音音高感知的影响。尽管几乎所有受试者都能显著高于机会水平地对语音性别进行分类，但音高排序因人而异。总体而言，载波率并未显著影响语音音高排序或语音性别分类：只要载波率至少是基频的两倍，或者当最低的 250 pps 载波的刺激脉冲与 F0 峰值对齐时。这些结果表明，当使用新型策略（如 STEP）对调制和脉冲定时进行良好控制时，载波率低至 250 pps/通道也足以支持对时间音高线索敏感的 CI 用户的功能语音音高感知。
