Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington, USA.
Ear Hear. 2019 Mar/Apr;40(2):295-311. doi: 10.1097/AUD.0000000000000615.
Channel interaction, the stimulation of overlapping populations of auditory neurons by distinct cochlear implant (CI) channels, likely limits the speech perception performance of CI users. This study examined the role of vocoder-simulated channel interaction in the ability of children with normal hearing (cNH) and adults with normal hearing (aNH) to recognize spectrally degraded speech. The primary aim was to determine the interaction between number of processing channels and degree of simulated channel interaction on phoneme identification performance as a function of age for cNH and to relate those findings to aNH and to CI users.
Medial vowel and consonant identification of cNH (age 8-17 years) and young aNH were assessed under six (for children) or nine (for adults) different conditions of spectral degradation. Stimuli were processed using a noise-band vocoder with 8, 12, and 15 channels and synthesis filter slopes of 15 (aNH only), 30, and 60 dB/octave (all NH subjects). Steeper filter slopes (larger numbers) simulated less electrical current spread and, therefore, less channel interaction. Spectrally degraded performance of the NH listeners was also compared with the unprocessed phoneme identification of school-aged children and adults with CIs.
Spectrally degraded phoneme identification improved as a function of age for cNH. For vowel recognition, cNH exhibited an interaction between the number of processing channels and vocoder filter slope, whereas aNH did not. Specifically, for cNH, increasing the number of processing channels only improved vowel identification in the steepest filter slope condition. Additionally, cNH were more sensitive to changes in filter slope. As the filter slopes increased, cNH continued to receive vowel identification benefit beyond where aNH performance plateaued or reached ceiling. For all NH participants, consonant identification improved with increasing filter slopes but was unaffected by the number of processing channels. Although cNH made more phoneme identification errors overall, their phoneme error patterns were similar to aNH. Furthermore, consonant identification of adults with CI was comparable to aNH listening to simulations with shallow filter slopes (15 dB/octave). Vowel identification of earlier-implanted pediatric ears was better than that of later-implanted ears and more comparable to cNH listening in conditions with steep filter slopes (60 dB/octave).
Recognition of spectrally degraded phonemes improved when simulated channel interaction was reduced, particularly for children. cNH showed an interaction between number of processing channels and filter slope for vowel identification. The differences observed between cNH and aNH suggest that identification of spectrally degraded phonemes continues to improve through adolescence and that children may benefit from reduced channel interaction beyond where adult performance has plateaued. Comparison to CI users suggests that early implantation may facilitate development of better phoneme discrimination.
通道交互作用，即通过不同的人工耳蜗（CI）通道刺激重叠的听神经元群体，可能会限制 CI 用户的言语感知表现。本研究旨在研究语音编码器模拟的通道交互作用在正常听力儿童（cNH）和正常听力成人（aNH）识别频谱失真语音方面的作用。主要目的是确定 cNH 的处理通道数量和模拟通道交互作用程度之间的相互作用如何随年龄变化影响语音识别表现，并将这些发现与 aNH 和 CI 用户联系起来。
对 8-17 岁的 cNH 和年轻的 aNH 进行中元音和辅音的识别，评估条件为 6 种（儿童）或 9 种（成人）不同的频谱退化程度。使用噪声带语音编码器处理刺激，具有 8、12 和 15 个通道，合成滤波器斜率为 15（仅 aNH）、30 和 60 dB/倍频程（所有 NH 受试者）。滤波器斜率越陡（数字越大）模拟的电流扩散越小，因此通道交互作用越小。还将 NH 听众的频谱退化语音识别性能与使用 CI 的学龄儿童和成人未经处理的语音识别进行了比较。
cNH 的频谱退化语音识别表现随年龄增长而提高。对于元音识别，cNH 表现出处理通道数量和语音编码滤波器斜率之间的相互作用，而 aNH 则没有。具体来说，对于 cNH，增加处理通道数量仅在最陡滤波器斜率条件下提高了元音识别。此外，cNH 对滤波器斜率的变化更敏感。随着滤波器斜率的增加，cNH 继续获得元音识别收益，而 aNH 的表现则达到平台或达到上限。对于所有 NH 参与者，随着滤波器斜率的增加，辅音识别得到改善，但不受处理通道数量的影响。尽管 cNH 整体上犯了更多的语音识别错误，但他们的语音错误模式与 aNH 相似。此外，CI 使用者的辅音识别与 aNH 收听斜率较浅的滤波器（15 dB/倍频程）的情况相似。较早植入的儿科耳朵的元音识别要好于较晚植入的耳朵，并且与 cNH 在滤波器斜率较陡的条件（60 dB/倍频程）下的识别更相似。
当模拟通道交互作用减少时，频谱失真语音的识别得到改善，尤其是对于儿童。cNH 表现出处理通道数量和滤波器斜率之间的元音识别相互作用。cNH 和 aNH 之间的差异表明，通过青少年时期，对频谱失真语音的识别能力继续提高，并且儿童可能会受益于减少的通道交互作用，超过了成人的表现平台。与 CI 用户的比较表明，早期植入可能有助于更好地发展语音辨别能力。
