Zhong Ziwei, Henry Kenneth S, Heinz Michael G
Weldon School of Biomedical Engineering, Purdue University, 206 South Martin Jischke Drive, West Lafayette, IN 47907, USA.
Department of Speech, Language, and Hearing Sciences, Purdue University, 500 Oval Drive, West Lafayette, IN 47907, USA.
Hear Res. 2014 Mar;309:55-62. doi: 10.1016/j.heares.2013.11.006. Epub 2013 Dec 4.
People with sensorineural hearing loss often have substantial difficulty understanding speech under challenging listening conditions. Behavioral studies suggest that reduced sensitivity to the temporal structure of sound may be responsible, but underlying neurophysiological pathologies are incompletely understood. Here, we investigate the effects of noise-induced hearing loss on coding of envelope (ENV) structure in the central auditory system of anesthetized chinchillas. ENV coding was evaluated noninvasively using auditory evoked potentials recorded from the scalp surface in response to sinusoidally amplitude modulated tones with carrier frequencies of 1, 2, 4, and 8 kHz and a modulation frequency of 140 Hz. Stimuli were presented in quiet and in three levels of white background noise. The latency of scalp-recorded ENV responses was consistent with generation in the auditory midbrain. Hearing loss amplified neural coding of ENV at carrier frequencies of 2 kHz and above. This result may reflect enhanced ENV coding from the periphery and/or an increase in the gain of central auditory neurons. In contrast to expectations, hearing loss was not associated with a stronger adverse effect of increasing masker intensity on ENV coding. The exaggerated neural representation of ENV information shown here at the level of the auditory midbrain helps to explain previous findings of enhanced sensitivity to amplitude modulation in people with hearing loss under some conditions. Furthermore, amplified ENV coding may potentially contribute to speech perception problems in people with cochlear hearing loss by acting as a distraction from more salient acoustic cues, particularly in fluctuating backgrounds.
感音神经性听力损失患者在具有挑战性的聆听条件下往往难以理解言语。行为学研究表明，对声音时间结构的敏感度降低可能是原因所在，但潜在的神经生理病理学机制尚未完全明了。在此，我们研究噪声性听力损失对麻醉的毛丝鼠中枢听觉系统中包络（ENV）结构编码的影响。通过记录头皮表面对载波频率为1、2、4和8kHz且调制频率为140Hz的正弦调幅音的听觉诱发电位，以非侵入性方式评估ENV编码。刺激在安静环境以及三种强度的白色背景噪声中呈现。头皮记录的ENV反应潜伏期与听觉中脑的产生一致。听力损失增强了2kHz及以上载波频率处的ENV神经编码。这一结果可能反映了外周ENV编码的增强和/或中枢听觉神经元增益的增加。与预期相反，听力损失与掩蔽强度增加对ENV编码的更强不利影响无关。此处显示的听觉中脑水平上ENV信息的夸张神经表征有助于解释先前在某些条件下听力损失患者对调幅敏感度增强的研究结果。此外，增强的ENV编码可能通过分散对更显著声学线索的注意力，尤其是在波动背景下，从而潜在地导致耳蜗性听力损失患者的言语感知问题。
