Van Wanrooij Marc M, Van Opstal A John
Department of Biophysics, Radboud University Nijmegen, Geert Grooteplein 21, 6525 EZ Nijmegen, The Netherlands.
J Neurophysiol. 2007 Jan;97(1):715-26. doi: 10.1152/jn.00260.2006. Epub 2006 Oct 25.
This paper reports on the acute effects of a monaural plug on directional hearing in the horizontal (azimuth) and vertical (elevation) planes of human listeners. Sound localization behavior was tested with rapid head-orienting responses toward brief high-pass filtered (>3 kHz; HP) and broadband (0.5-20 kHz; BB) noises, with sound levels between 30 and 60 dB, A-weighted (dBA). To deny listeners any consistent azimuth-related head-shadow cues, stimuli were randomly interleaved. A plug immediately degraded azimuth performance, as evidenced by a sound level-dependent shift ("bias") of responses contralateral to the plug, and a level-dependent change in the slope of the stimulus-response relation ("gain"). Although the azimuth bias and gain were highly correlated, they could not be predicted from the plug's acoustic attenuation. Interestingly, listeners performed best for low-intensity stimuli at their normal-hearing side. These data demonstrate that listeners rely on monaural spectral cues for sound-source azimuth localization as soon as the binaural difference cues break down. Also the elevation response components were affected by the plug: elevation gain depended on both stimulus azimuth and on sound level and, as for azimuth, localization was best for low-intensity stimuli at the hearing side. Our results show that the neural computation of elevation incorporates a binaural weighting process that relies on the perceived, rather than the actual, sound-source azimuth. It is our conjecture that sound localization ensues from a weighting of all acoustic cues for both azimuth and elevation, in which the weights may be partially determined, and rapidly updated, by the reliability of the particular cue.
本文报告了单耳耳塞对人类听众在水平（方位角）和垂直（仰角）平面上定向听力的急性影响。通过对短暂的高通滤波（>3 kHz；HP）和宽带（0.5 - 20 kHz；BB）噪声做出快速转头反应来测试声音定位行为，声音水平在30至60 dB之间，A加权（dBA）。为了使听众无法获得任何与方位角相关的一致的头部阴影线索，刺激是随机交错呈现的。耳塞会立即降低方位角表现，这表现为与耳塞对侧的反应出现与声级相关的偏移（“偏差”），以及刺激 - 反应关系斜率的与声级相关的变化（“增益”）。尽管方位角偏差和增益高度相关，但无法根据耳塞的声学衰减来预测它们。有趣的是，听众在正常听力一侧对低强度刺激的表现最佳。这些数据表明，一旦双耳差异线索失效，听众就会依赖单耳频谱线索进行声源方位角定位。仰角反应成分也受到耳塞的影响：仰角增益既取决于刺激方位角，也取决于声级，并且与方位角情况一样，在听力一侧对低强度刺激的定位最佳。我们的结果表明，仰角的神经计算包含一个双耳加权过程，该过程依赖于感知到的而非实际的声源方位角。我们推测，声音定位是通过对方位角和仰角的所有声学线索进行加权而产生的，其中权重可能部分由特定线索的可靠性决定，并迅速更新。
