The Sound Source Distance Dependence of the Acoustical Cues to Location and Their Encoding by Neurons in the Inferior Colliculus: Implications for the Duplex Theory
The Sound Source Distance Dependence of the Acoustical Cues to Location and Their Encoding by Neurons in the Inferior Colliculus: Implications for the Duplex Theory
复制标题
DOI：
10.1007/978-1-4614-1590-9_31
复制
发表时间：
2013-01-01
期刊：
影响因子：
--
通讯作者：
Tollin, Daniel J.
中科院分区：
文献类型：
--
作者：
Jones, Heath G.;Koka, Kanthaiah;Tollin, Daniel J.
世纪以来，双工理论认为低频和高频声音分别使用两种不同的声学线索，即耳间时间（ITD）和水平（ILD）差异进行定位。心理物理学的数据普遍支持纯音理论。在解剖学上，ITD和ILD在两个平行的脑干通路中分别编码。声学ILD是位置和频率的函数，使得较低和较高频率分别表现出较小和较大的ILD。已经确定，整个听觉神经轴的神经元编码高频ILD。在声学上，低频ILD可以忽略不计（类似于1-2 dB）;然而，人类仍然对它们敏感，生理学研究经常报告低频ILD敏感神经元。这些发现与双重理论不一致。我们认为，这些差异产生的声学环境的特性不足。我们假设，低频ILD变得大而有用时，源位于头部附近。我们通过测量龙猫的ILD作为源距离的函数和下丘（IC）103个神经元对ILD的敏感性来验证这一假设。IC神经元的ILD敏感性被发现是频率无关的，即使远场声ILD是频率依赖的。然而，随着源距离的减小，低频ILD的幅度增加。使用信息论的方法，我们证明了一个人口的IC神经元可以编码的整个频率，将经历作为一个联合函数的源位置和距离的声学ILD的全范围。
For over a century, the Duplex theory has posited that low- and high-frequency sounds are localized using two different acoustical cues, interaural time (ITDs) and level (ILDs) differences, respectively. Psychophysical data have generally supported the theory for pure tones. Anatomically, ITDs and ILDs are separately encoded in two parallel brainstem pathways. Acoustically ILDs are a function of location and frequency such that lower and higher frequencies exhibit smaller and larger ILDs, respectively. It is well established that neurons throughout the auditory neuraxis encode high-frequency ILDs. Acoustically, low-frequency ILDs are negligible (similar to 1-2 dB); however, humans are still sensitive to them and physiological studies often report low-frequency ILD-sensitive neurons. These latter findings are at odds with the Duplex theory. We suggest that these discrepancies arise from an inadequate characterization of the acoustical environment. We hypothesize that low-frequency ILDs become large and useful when sources are located near the head. We tested this hypothesis by making measurements of the ILDs in chinchillas as a function of source distance and the sensitivity to ILDs in 103 neurons in the inferior colliculus (IC). The ILD sensitivity of IC neurons was found to be frequency independent even though far-field acoustical ILDs were frequency dependent. However, as source distance was decreased, the magnitudes of low-frequency ILDs increased. Using information theoretic methods, we demonstrate that a population of IC neurons can encode the full range of acoustic ILDs across frequency that would be experienced as a joint function of source location and distance.