Joris P X, Schreiner C E, Rees A
Laboratory of Auditory Neurophysiology, K.U. Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium.
Physiol Rev. 2004 Apr;84(2):541-77. doi: 10.1152/physrev.00029.2003.
Amplitude modulation (AM) is a temporal feature of most natural acoustic signals. A long psychophysical tradition has shown that AM is important in a variety of perceptual tasks, over a range of time scales. Technical possibilities in stimulus synthesis have reinvigorated this field and brought the modulation dimension back into focus. We address the question whether specialized neural mechanisms exist to extract AM information, and thus whether consideration of the modulation domain is essential in understanding the neural architecture of the auditory system. The available evidence suggests that this is the case. Peripheral neural structures not only transmit envelope information in the form of neural activity synchronized to the modulation waveform but are often tuned so that they only respond over a limited range of modulation frequencies. Ascending the auditory neuraxis, AM tuning persists but increasingly takes the form of tuning in average firing rate, rather than synchronization, to modulation frequency. There is a decrease in the highest modulation frequencies that influence the neural response, either in average rate or synchronization, as one records at higher and higher levels along the neuraxis. In parallel, there is an increasing tolerance of modulation tuning for other stimulus parameters such as sound pressure level, modulation depth, and type of carrier. At several anatomical levels, consideration of modulation response properties assists the prediction of neural responses to complex natural stimuli. Finally, some evidence exists for a topographic ordering of neurons according to modulation tuning. The picture that emerges is that temporal modulations are a critical stimulus attribute that assists us in the detection, discrimination, identification, parsing, and localization of acoustic sources and that this wide-ranging role is reflected in dedicated physiological properties at different anatomical levels.
幅度调制（AM）是大多数自然声信号的一种时间特征。长期以来的心理物理学传统表明，在一系列时间尺度上，AM在各种感知任务中都很重要。刺激合成方面的技术可能性为该领域注入了新的活力，并使调制维度重新成为焦点。我们探讨是否存在专门的神经机制来提取AM信息，以及因此在理解听觉系统的神经结构时，考虑调制域是否至关重要。现有证据表明情况确实如此。外周神经结构不仅以与调制波形同步的神经活动形式传递包络信息，而且通常经过调谐，使得它们仅在有限的调制频率范围内做出反应。沿着听觉神经轴向上，AM调谐持续存在，但越来越多地表现为平均放电率对调制频率的调谐，而不是同步。随着在神经轴上越来越高的水平进行记录，影响神经反应的最高调制频率在平均放电率或同步方面都有所降低。同时，对于其他刺激参数，如声压级、调制深度和载波类型，调制调谐的耐受性也在增加。在几个解剖学层面，考虑调制反应特性有助于预测对复杂自然刺激的神经反应。最后，有一些证据表明神经元根据调制调谐存在拓扑排序。呈现出的情况是，时间调制是一种关键的刺激属性，有助于我们进行声源的检测、辨别、识别、解析和定位，并且这种广泛的作用反映在不同解剖学层面的专门生理特性中。
