Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
Eur J Neurosci. 2014 Jan;39(2):197-206. doi: 10.1111/ejn.12402. Epub 2013 Oct 28.
For over a century, the duplex theory has guided our understanding of human sound localization in the horizontal plane. According to this theory, the auditory system uses interaural time differences (ITDs) and interaural level differences (ILDs) to localize low-frequency and high-frequency sounds, respectively. Whilst this theory successfully accounts for the localization of tones by humans, some species show very different behaviour. Ferrets are widely used for studying both clinical and fundamental aspects of spatial hearing, but it is not known whether the duplex theory applies to this species or, if so, to what extent the frequency range over which each binaural cue is used depends on acoustical or neurophysiological factors. To address these issues, we trained ferrets to lateralize tones presented over earphones and found that the frequency dependence of ITD and ILD sensitivity broadly paralleled that observed in humans. Compared with humans, however, the transition between ITD and ILD sensitivity was shifted toward higher frequencies. We found that the frequency dependence of ITD sensitivity in ferrets can partially be accounted for by acoustical factors, although neurophysiological mechanisms are also likely to be involved. Moreover, we show that binaural cue sensitivity can be shaped by experience, as training ferrets on a 1-kHz ILD task resulted in significant improvements in thresholds that were specific to the trained cue and frequency. Our results provide new insights into the factors limiting the use of different sound localization cues and highlight the importance of sensory experience in shaping the underlying neural mechanisms.
一个多世纪以来，双工理论一直指导着我们对人类在水平面上声音定位的理解。根据该理论，听觉系统分别使用耳间时间差（ITD）和耳间水平差（ILD）来定位低频和高频声音。虽然该理论成功地解释了人类对音调的定位，但有些物种的表现却非常不同。雪貂被广泛用于研究空间听觉的临床和基础方面，但尚不清楚双工理论是否适用于该物种，如果适用，每种双耳线索的使用频率范围取决于声学还是神经生理学因素。为了解决这些问题，我们训练雪貂对耳机中呈现的音调进行定位，发现 ITD 和 ILD 敏感性的频率依赖性与在人类中观察到的大致相似。然而，与人类相比，ITD 和 ILD 敏感性之间的转换向更高的频率移动。我们发现，尽管神经生理学机制也可能参与其中，但雪貂的 ITD 敏感性的频率依赖性部分可以用声学因素来解释。此外，我们还表明，双耳线索敏感性可以通过经验来塑造，因为在 1 kHz ILD 任务上训练雪貂会导致对训练线索和频率具有特异性的阈值显著提高。我们的研究结果提供了对限制使用不同声音定位线索的因素的新见解，并强调了感官经验在塑造潜在神经机制方面的重要性。
