Biophysics Department, Donders Institute for Brain, Cognition, and Behaviour, Radboud University, 6525 AJ, Nijmegen, The Netherlands.
Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA.
Sci Rep. 2019 Feb 7;9(1):1642. doi: 10.1038/s41598-018-37537-z.
The brain estimates the two-dimensional direction of sounds from the pressure-induced displacements of the eardrums. Accurate localization along the horizontal plane (azimuth angle) is enabled by binaural difference cues in timing and intensity. Localization along the vertical plane (elevation angle), including frontal and rear directions, relies on spectral cues made possible by the elevation dependent filtering in the idiosyncratic pinna cavities. However, the problem of extracting elevation from the sensory input is ill-posed, since the spectrum results from a convolution between source spectrum and the particular head-related transfer function (HRTF) associated with the source elevation, which are both unknown to the system. It is not clear how the auditory system deals with this problem, or which implicit assumptions it makes about source spectra. By varying the spectral contrast of broadband sounds around the 6-9 kHz band, which falls within the human pinna's most prominent elevation-related spectral notch, we here suggest that the auditory system performs a weighted spectral analysis across different frequency bands to estimate source elevation. We explain our results by a model, in which the auditory system weighs the different spectral bands, and compares the convolved weighted sensory spectrum with stored information about its own HRTFs, and spatial prior assumptions.
大脑通过鼓膜的压力感应位移来估算二维声音方向。通过时间和强度的双耳差异线索，可以实现水平方向（方位角）的精确定位。垂直方向（仰角）的定位，包括前后方向，依赖于耳廓特有的、因仰角而异的滤波作用产生的频谱线索。然而，从感觉输入中提取仰角的问题是不适定的，因为频谱是由源频谱和与源仰角相关的特定头部相关传递函数（HRTF）之间的卷积产生的，而系统对这两者都一无所知。听觉系统如何处理这个问题，或者它对源频谱做出了哪些隐含假设，目前还不清楚。通过改变位于人类耳廓最显著的仰角相关频谱凹口内的 6-9 kHz 频带周围的宽带声音的频谱对比度，我们在此提出，听觉系统会在不同的频带之间进行加权频谱分析，以估计声源的仰角。我们通过一个模型来解释我们的结果，在该模型中，听觉系统对不同的频谱带进行加权，并将卷积后的加权感觉频谱与关于自身 HRTF 和空间先验假设的存储信息进行比较。
