Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, IN 47907, USA.
Adv Exp Med Biol. 2013;787:55-63. doi: 10.1007/978-1-4614-1590-9_7.
Physiological data show that preceding sound can reduce cochlear amplifier gain via the medial olivocochlear reflex (MOCR). Our laboratory has used forward masking as a tool to look for evidence of this effect psychophysically, which has led us to reassess mechanisms of forward masking. The traditional temporal window model (TWM) proposes that masking occurs via an excitatory mechanism that integrates within a temporal window. We propose that gain reduction may also contribute to forward masking. In our stimulus paradigm, growth of masking is measured with an off-frequency forward masker to estimate the basilar membrane input/output (I/O) function. The gain of the I/O function is reduced when an on-frequency precursor is introduced, consistent with a gain reduction hypothesis. Recently we explored the time course of this estimated gain reduction by examining the effect of precursor duration (Roverud and Strickland ). In that study, thresholds initially increased with increasing precursor duration, then decreased for longer durations. This result is not consistent with solely excitatory masking, but may reflect gain reduction by the MOCR. If the precursor is long enough, it could be influenced by the gain reduction it elicited. In the present study, we examine the effect of precursor duration with an on-frequency precursor and an off-frequency precursor. If intense enough, an off-frequency precursor may reduce gain at the signal frequency place. However, assuming it has no gain at the signal place, it would not be influenced by the reduction in gain, regardless of its duration. We developed a modified TWM that includes time-varying gain reduction by the precursor, resulting in an adapting I/O function. Results are modeled with the standard TWM and the TWM with gain reduction.
生理数据表明，前导音可以通过内侧橄榄耳蜗反射 (MOCR) 降低耳蜗放大器增益。我们实验室使用前向掩蔽作为一种工具，从心理物理学角度寻找这种效应的证据，这使我们重新评估了前向掩蔽的机制。传统的时间窗模型 (TWM) 提出，掩蔽是通过在时间窗内整合的兴奋性机制发生的。我们提出，增益降低也可能导致前向掩蔽。在我们的刺激范式中，使用离频前掩蔽器来测量掩蔽的增长，以估计基底膜输入/输出 (I/O) 函数。当引入同频前导时，I/O 函数的增益会降低，这与增益降低假说一致。最近，我们通过研究前导时长的影响来探索这种估计增益降低的时间进程（Roverud 和 Strickland）。在该研究中，随着前导时长的增加，阈值最初增加，然后对于更长的时长下降。这个结果与单纯的兴奋性掩蔽不一致，但可能反映了 MOCR 的增益降低。如果前导足够长，它可能会受到它引起的增益降低的影响。在本研究中，我们用同频前导和离频前导研究了前导时长的影响。如果强度足够大，离频前导可能会降低信号频率位置的增益。然而，假设它在信号位置没有增益，无论其时长如何，它都不会受到增益降低的影响。我们开发了一种改进的 TWM，其中包括前导的时变增益降低，从而产生自适应的 I/O 函数。使用标准 TWM 和具有增益降低的 TWM 对结果进行建模。
