Huang A Y, May B J
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21205-2196, USA.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2341-8. doi: 10.1121/1.417943.
Rice et al. [Hear. Res. 58, 132-152 (1992)] classified directional properties of the cat's head-related transfer function (HRTF) into three frequency domains. Low frequencies (< 5 kHz) display a broad azimuth-sensitive spectral peak that establishes interaural level differences, mid frequencies (5-18 kHz) are marked with a single deep spectral notch that changes in frequency as a function of both azimuth and elevation, and high frequencies (18-50 kHz) exhibit a complex pattern of peaks and notches that shows extensive but less systematic changes with sound location. Spectral cues conveyed by the mid frequencies of broadband sounds are important in tasks that require cats to identify the actual location of acoustic stimuli [Huang and May, J. Acoust. Soc. Am. (in press)]. The present study investigates how directional cues conveyed by the mid- and high-frequency spectrum of the HRTF influence the cat's ability to discriminate between sound locations. Thresholds for spatial acuity were measured as minimum audible angles (MAAs) [Mills, J. Acoust. Soc. Am. 30, 237-246 (1958)] at positive azimuths in the interaural horizontal plane and at positive and negative elevations in the median vertical plane. The frequency domain of the noise burst had little effect on MAAs in the horizontal plane, but removal of high-frequency spectral information significantly increased thresholds at positive and negative elevations in the median plane. These results suggest that cats are sensitive to directional properties of the HRTF at frequencies above 18 kHz and may use this information to detect small changes in sound source elevation.
赖斯等人[《听觉研究》58卷，第132 - 152页(1992年)]将猫的头部相关传递函数(HRTF)的方向特性划分为三个频域。低频(<5千赫)呈现出一个宽泛的方位敏感频谱峰值，该峰值确立了双耳声级差；中频(5 - 18千赫)的特征是有一个单一的深频谱凹陷，其频率会随着方位和仰角的变化而改变；高频(18 - 50千赫)呈现出复杂的峰值和凹陷模式，随着声音位置的变化，这种模式会发生广泛但不太系统的改变。宽带声音中频所传达的频谱线索在要求猫识别声学刺激实际位置的任务中很重要[黄和梅，《美国声学学会杂志》(即将发表)]。本研究调查了HRTF的中高频频谱所传达的方向线索如何影响猫区分声音位置的能力。空间敏锐度的阈值以最小可听角度(MAAs)[米尔斯，《美国声学学会杂志》30卷，第237 - 246页(1958年)]来衡量，测量在双耳水平面的正方位以及正中垂直面的正负仰角处进行。噪声突发的频域对水平面的MAAs影响很小，但去除高频频谱信息会显著提高正中平面正负仰角处的阈值。这些结果表明，猫对18千赫以上频率的HRTF方向特性敏感，并且可能利用这些信息来检测声源仰角的微小变化。
