OFFSET AP MASKER TUNING CURVE AND THE FFT OF THE STIMULUS
OFFSET AP MASKER TUNING CURVE AND THE FFT OF THE STIMULUS
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DOI：
10.1121/1.396634
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发表时间：
1988-10-01
影响因子：
2.4
通讯作者：
LEWIS, ER
中科院分区：
文献类型：
--
作者：
HENRY, KR;LEWIS, ER
在之前的实验中，人们注意到，耳蜗复合动作电位（CAP）可以通过音调的偏移产生，前提是音调的幅度由梯形调制，梯形的斜率通常比产生起始响应所需的斜率要陡得多。随后，这种具有陡峭斜率的梯形音脉冲被用作同步和前向掩蔽实验中的探针刺激，这些实验旨在评估这些偏移 CAP 的调谐特性。 通过绘制将偏移 CAP 幅度降低 50% 所需的掩蔽频率来生成掩蔽调谐曲线 (MTC)。同时掩蔽偏移 CAP 生成了 W 形 MTC，具有两个急剧调谐的尖端和一个急剧调谐的峰值。前向掩蔽产生了急剧调谐的 V 形偏移 MTC。相比之下，对于起始 CAP，同时和前向掩蔽都会生成 V 形 MTC。产生偏移 CAP 所需的非常陡峭的刺激斜率可能比产生起始 CAP 所需的更平缓的斜率产生更多的声学飞溅，并且这可能与起始和偏移同时 MTC 的不同形状有关。为了探索这种可能性，研究了光谱特性（通过快速傅里叶变换或 FFT 确定）与 MTC 形状的关系。在所描述的实验中，FFT 的形状通过三种方法改变：（1）改变探针刺激持续时间，从而改变相对于音调的飞溅功率； (2)使用过滤噪声代替纯音作为探针刺激； (3)改变探针刺激的上升和衰减（r和d）时间，从而改变声学飞溅的绝对功率。这些实验证明了在探针激励的 FFT 宽度发生大范围变化的情况下，偏移 MTC 的形状具有鲁棒性。偏移 MTC 形状的两个关键决定因素是探针刺激的主频率和用于生成偏移 MTC 的掩蔽器类型（同步与前向）。我们的观察还表明，偏移同步 MTC 的 W 形状可能是由于探针刺激水平较高而沿基底膜激活发生变化的结果。
In previous experiments, it was noted that a cochlear compound action potential (CAP) can be produced by the offset of a tone, provided that the amplitude of the tone is modulated by a trapezoid with slopes that are typically much steeper than required to produce onset responses. Subsequently, such trapezoidal tone bursts with steep slopes were used as probe stimuli in simultaneous and forward masking experiments that were designed to evaluate the tuning characteristics of these offset CAPs. Masker tuning curves (MTCs) were generated by plotting the masker frequency necessary to reduce the amplitude of the offset CAP by 50%. Simultaneous masking of the offset CAP generated a W-shaped MTC, with two sharply tuned tips and one sharply tuned peak. Forward masking generated a sharply tuned V-shaped offset MTC. By contrast, for onset CAPs, both simultaneous and forward masking generated V-shaped MTCs. They very steep stimulus slopes required to produce an offset CAP are likely to generate much more acoustic splatter than the more gradual slopes required to produce an onset CAP, and this may be related to the different shapes of the onset and offset simultaneous MTCs. To explore this possibility, the relationship of the spectral characteristics (determined by fast Fourier transform, or FFT) to the shape of the MTC was studied. The shapes of the FFT were changed by three methods in the described experiments: (1) The probe stimulus duration was varied, thereby changing the power of the splatter, relative to that of the tone; (2) filtered noise was used instead of a pure tone as the probe stimulus; and (3) the rise and decay (r and d) time of the probe stimulus was altered, thereby changing the absolute power of the acoustic splatter. These experiments demonstrate robustness of the shape of the offset MTC under a wide range of changes in the width of the FFT of the probe stimulus. Two crucial determinants of the shape of the offset MTC are the dominant frequency of the probe stimulus and the type of masker (simultaneous versus forward) used to generate the offset MTC. Our observations also suggest that the W shape of the offset simultaneous MTC might be a consequence of a shift of activation along the basilar membrane due to the moderately high level of the probe stimulus.