Human bilateral cochlear implant users do poorly on tasks involving interaural time differences (ITD), a cue that provides important benefits to the normal hearing, especially in challenging acoustic environments, yet the precision of neural ITD coding in acutely deafened, bilaterally implanted cats is essentially normal (Smith and Delgutte, 2007a). One explanation for this discrepancy is that the extended periods of binaural deprivation typically experienced by cochlear implant users degrades neural ITD sensitivity, by either impeding normal maturation of the neural circuitry or altering it later in life. To test this hypothesis, we recorded from single units in inferior colliculus of two groups of bilaterally implanted, anesthetized cats that contrast maximally in binaural experience: acutely deafened cats, which had normal binaural hearing until experimentation, and congenitally deaf white cats, which received no auditory inputs until the experiment. Rate responses of only half as many neurons showed significant ITD sensitivity to low-rate pulse trains in congenitally deaf cats compared with acutely deafened cats. For neurons that were ITD sensitive, ITD tuning was broader and best ITDs were more variable in congenitally deaf cats, leading to poorer ITD coding within the naturally occurring range. A signal detection model constrained by the observed physiology supports the idea that the degraded neural ITD coding resulting from deprivation of binaural experience contributes to poor ITD discrimination by human implantees.
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机译：人类双侧人工耳蜗使用者在涉及耳间时差（ITD）的任务上做得很差，这一提示为正常的听力提供了重要的好处，尤其是在具有挑战性的声学环境中，但是在严重耳聋，双侧植入的猫中，神经ITD编码的准确性基本上是正常（Smith and Delgutte，2007a）。对此差异的一种解释是，人工耳蜗植入用户通常经历的双耳剥夺时间延长，会阻碍神经电路的正常成熟或在以后的生活中改变它，从而降低神经ITD敏感性。为了检验这一假设，我们从两组双侧植入的麻醉猫的下丘的单个单元中记录了双耳经验的最大差异：急性耳聋的猫，双耳听力正常，直到实验为止；先天性聋的白猫，没有接受任何实验听觉输入直到实验。与先天性失聪猫相比，先天性聋猫中只有一半神经元的速率响应显示出对低速率脉冲序列具有显着的ITD敏感性。对于对ITD敏感的神经元，ITD调节范围更广，最好的ITD在先天性聋猫中的变化更大，从而导致在自然发生的范围内ITD编码较差。受所观察到的生理学限制的信号检测模型支持这样的观点，即由于双耳经验的剥夺而导致的退化的神经ITD编码会导致人类植入者的ITD辨别能力差。
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