Adel Youssef, Hilkhuysen Gaston, Noreña Arnaud, Cazals Yves, Roman Stéphane, Macherey Olivier
Aix Marseille Université, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla CS 40006, 13453, Marseille Cedex 13, France.
Audiological Acoustics, Department of Otorhinolaryngology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
J Assoc Res Otolaryngol. 2017 Jun;18(3):495-512. doi: 10.1007/s10162-016-0613-5. Epub 2017 Feb 21.
Electrical stimulation of auditory nerve fibers using cochlear implants (CI) shows psychophysical forward masking (pFM) up to several hundreds of milliseconds. By contrast, recovery of electrically evoked compound action potentials (eCAPs) from forward masking (eFM) was shown to be more rapid, with time constants no greater than a few milliseconds. These discrepancies suggested two main contributors to pFM: a rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures. In the present study, we investigate whether the use of different maskers between eCAP and psychophysical measures, specifically single-pulse versus pulse train maskers, may have been a source of confound.In experiment 1, we measured eFM using the following: a single-pulse masker, a 300-ms low-rate pulse train masker (LTM, 250 pps), and a 300-ms high-rate pulse train masker (HTM, 5000 pps). The maskers were presented either at same physical current (Φ) or at same perceptual (Ψ) level corresponding to comfortable loudness. Responses to a single-pulse probe were measured for masker-probe intervals ranging from 1 to 512 ms. Recovery from masking was much slower for pulse trains than for the single-pulse masker. When presented at Φ level, HTM produced more and longer-lasting masking than LTM. However, results were inconsistent when LTM and HTM were compared at Ψ level. In experiment 2, masked detection thresholds of single-pulse probes were measured using the same pulse train masker conditions. In line with our eFM findings, masked thresholds for HTM were higher than those for LTM at Φ level. However, the opposite result was found when the pulse trains were presented at Ψ level.Our results confirm the presence of slow-recovery phenomena at the level of the auditory nerve in CI users, as previously shown in animal studies. Inconsistencies between eFM and pFM results, despite using the same masking conditions, further underline the importance of comparing electrophysiological and psychophysical measures with identical stimulation paradigms.
使用人工耳蜗（CI）对听神经纤维进行电刺激时，会出现长达数百毫秒的心理物理学前掩蔽（pFM）。相比之下，电诱发复合动作电位（eCAP）从前掩蔽（eFM）中的恢复则更快，时间常数不超过几毫秒。这些差异表明，pFM主要有两个影响因素：一个是由于听神经的不应期特性导致的快速恢复过程，另一个是源于更中枢结构的缓慢恢复过程。在本研究中，我们探究了在eCAP和心理物理学测量中使用不同掩蔽刺激，特别是单脉冲掩蔽刺激与脉冲序列掩蔽刺激，是否可能是造成混淆的一个原因。在实验1中，我们使用以下刺激测量eFM：单脉冲掩蔽刺激、300毫秒的低速率脉冲序列掩蔽刺激（LTM，250次/秒）和300毫秒的高速率脉冲序列掩蔽刺激（HTM，5000次/秒）。掩蔽刺激以相同的物理电流（Φ）或对应舒适响度的相同感知（Ψ）水平呈现。测量了掩蔽刺激 - 探测刺激间隔从1到512毫秒时对单脉冲探测刺激的反应。脉冲序列的掩蔽恢复比单脉冲掩蔽刺激慢得多。当以Φ水平呈现时，HTM产生的掩蔽作用比LTM更多且持续时间更长。然而，当在Ψ水平比较LTM和HTM时，结果并不一致。在实验2中，使用相同的脉冲序列掩蔽刺激条件测量单脉冲探测刺激的掩蔽检测阈值。与我们的eFM研究结果一致，在Φ水平时，HTM的掩蔽阈值高于LTM。然而，当以Ψ水平呈现脉冲序列时，结果却相反。我们的结果证实了人工耳蜗使用者听神经水平存在缓慢恢复现象，正如先前在动物研究中所显示的那样。尽管使用了相同的掩蔽条件，但eFM和pFM结果之间的不一致进一步强调了采用相同刺激范式比较电生理测量和心理物理学测量的重要性。
