Pressnitzer D, Winter I M, Patterson R D
Centre for the Neural Basis of Hearing, The Physiological Laboratory, Downing Street, CB2 3EG England, Cambridge, UK.
Hear Res. 2000 Nov;149(1-2):155-66. doi: 10.1016/s0378-5955(00)00175-1.
Human listeners hear an asymmetry in the perception of damped and ramped sinusoids; the partial loudness of the envelope component is greater than the partial loudness of the carrier component for damped sinusoids. Here we show that an asymmetry also occurs in the physiological responses of most units in the ventral cochlear nucleus to these same sounds. The activity elicited by damped sinusoids is mainly restricted to the beginning of each envelope period, which is not the case for ramped sinusoids. This can be quantified by computing the ratio of the tallest bin of the modulation period histogram to the total number of spikes (the peak-to-total ratio, p/t). Damped sinusoids produce a higher p/t than ramped sinusoids, which demonstrates physiological temporal asymmetry. It is also the case that ramped sinusoids typically elicit more spikes than damped sinusoids. The physiological asymmetry occurs where the perceptual asymmetry is present. It is maximal at modulation half-lives of 4 and 16 ms, greatly reduced at 1 ms and absent at 64 ms. Different unit types exhibit differing degrees of temporal asymmetry. Onset units produce the greatest p/t asymmetry, primary-like units produce the least asymmetry and chopper units are in-between. With regard to total spike count, the maximal asymmetry occurs with chopper units. If primary-like units are assumed to reflect the activity in primary auditory nerve fibres, then there is enhancement of temporal asymmetry in the ventral cochlear nucleus by both onset and chopper units.
人类听众在感知阻尼和斜升正弦波时会察觉到一种不对称性；对于阻尼正弦波，包络成分的部分响度大于载波成分的部分响度。在这里，我们表明，腹侧耳蜗核中大多数神经元对这些相同声音的生理反应也存在不对称性。阻尼正弦波引发的活动主要局限于每个包络周期的开始阶段，而斜升正弦波则不然。这可以通过计算调制周期直方图中最高的直方条与总尖峰数的比值（峰谷比，p/t）来量化。阻尼正弦波产生的p/t比斜升正弦波更高，这表明存在生理时间不对称性。同样，斜升正弦波通常比阻尼正弦波引发更多的尖峰。生理不对称性出现在感知不对称性存在的地方。在调制半衰期为4毫秒和16毫秒时最大，在1毫秒时大大降低，在64毫秒时不存在。不同类型的神经元表现出不同程度的时间不对称性。起始神经元产生的p/t不对称性最大，初级样神经元产生的不对称性最小，切波神经元则介于两者之间。就总尖峰数而言，最大不对称性出现在切波神经元中。如果假设初级样神经元反映初级听神经纤维的活动，那么起始神经元和切波神经元都会增强腹侧耳蜗核中的时间不对称性。
