Su T I, Recanzone G H
Center for Neuroscience, University of California at Davis, 95616, USA.
J Assoc Res Otolaryngol. 2001 Sep;2(3):246-56. doi: 10.1007/s101620010073.
The ability of humans to localize sounds remains relatively constant across a range of intensities well above detection threshold, and increasing the spectral content of the stimulus results in an improvement in localization ability. For broadband stimuli, intensities near detection threshold result in fewer and weaker binaural cues used in azimuth localization because the stimulus energy at the high- and low-frequency ends of the audible spectrum fall below detection threshold. Thus, the ability to localize broadband sounds in azimuth is predicted to be degraded at audible but near threshold stimulus intensities. The spectral cues for elevation localization (spectral peaks and notches generated by the head-related transfer function) span a narrower frequency range than those for azimuth. As the stimulus intensity decreases, the ability to detect the stimulus frequencies corresponding to the spectral notches will be more strongly affected than the ability to detect frequencies outside the range where these spectral cues are useful. Consequently, decreasing the stimulus intensity should degrade localization in both azimuth and elevation and create a greater deficit in elevation localization due to the narrower band of audible frequencies containing elevation cues compared to azimuth cues. The present study measured the ability of 11 normal human subjects to localize broadband noise stimuli along the midsagittal plane and horizontal meridian at stimulus intensities of 14, 22, and 30 dB above the subject's detection threshold using a go/no-go behavioral paradigm. Localization ability decreased in both azimuth and elevation with decreasing stimulus intensity, and this effect was greater on localization in elevation than on localization in azimuth. The differential effects of stimulus intensity on sound localization in azimuth and elevation found in the present study may provide a valuable tool in investigating the neural correlates of sound location perception.
在远高于检测阈值的一系列强度范围内，人类定位声音的能力保持相对恒定，并且增加刺激的频谱内容会导致定位能力的提高。对于宽带刺激，接近检测阈值的强度会导致在方位定位中使用的双耳线索更少且更弱，因为可听频谱的高频和低频端的刺激能量低于检测阈值。因此，预计在可听但接近阈值的刺激强度下，在方位上定位宽带声音的能力会下降。用于仰角定位的频谱线索（由头部相关传递函数产生的频谱峰值和凹陷）所跨越的频率范围比用于方位定位的频谱线索更窄。随着刺激强度降低，检测与频谱凹陷相对应的刺激频率的能力将比检测这些频谱线索有用范围之外的频率的能力受到更强的影响。因此，降低刺激强度应会降低方位和仰角的定位能力，并且由于与方位线索相比，包含仰角线索的可听频率带更窄，因此在仰角定位中会产生更大的缺陷。本研究使用“是/否”行为范式，测量了11名正常人类受试者在高于受试者检测阈值14、22和30分贝的刺激强度下，沿矢状中平面和水平子午线定位宽带噪声刺激的能力。随着刺激强度降低，方位和仰角的定位能力均下降，并且这种影响在仰角定位上比在方位定位上更大。本研究中发现的刺激强度对方位和仰角声音定位的不同影响，可能为研究声音位置感知的神经相关性提供一个有价值的工具。
