Ebert Charles S, Blanks Deidra A, Patel Mihir R, Coffey Charles S, Marshall Allen F, Fitzpatrick Douglas C
Department of Otolaryngology - Head and Neck Surgery, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7070, USA.
Hear Res. 2008 Jan;235(1-2):134-42. doi: 10.1016/j.heares.2007.11.003. Epub 2007 Nov 23.
An important cue for sound localization and separation of signals from noise is the interaural time difference (ITD). Humans are able to localize sounds within 1-2 degrees and can detect very small changes in the ITD (10-20micros). In contrast, many animals localize sounds with less precision than humans. Rabbits, for example, have sound localization thresholds of approximately 22 degrees . There is only limited information about behavioral ITD discrimination in animals with poor sound localization acuity that are typically used for the neural recordings. For this study, we measured behavioral discrimination of ITDs in the rabbit for a range of reference ITDs from 0 to +/-300micros. The behavioral task was conditioned avoidance and the stimulus was band-limited noise (500-1500Hz). Across animals, the average discrimination threshold was 50-60micros for reference ITDs of 0 to +/-200micros. There was no trend in the thresholds across this range of reference ITDs. For a reference ITD of +/-300micros, which is near the limit of the physiological window defined by the head width in this species, the discrimination threshold increased to approximately 100micros. The ITD discrimination in rabbits less acute than in cats, which have a similar head size. This result supports the suggestion that ITD discrimination, like sound localization [see Heffner, 1997. Acta Otolaryngol. 532 (Suppl.), 46-53] is determined by factors other than head size.
声音定位以及从噪声中分离信号的一个重要线索是双耳时间差（ITD）。人类能够在1 - 2度范围内定位声音，并且能够检测到ITD中非常小的变化（10 - 20微秒）。相比之下，许多动物定位声音的精度不如人类。例如，兔子的声音定位阈值约为22度。对于通常用于神经记录的声音定位敏锐度较差的动物，关于其行为ITD辨别能力的信息非常有限。在本研究中，我们测量了兔子在0至±300微秒范围内一系列参考ITD下的行为ITD辨别能力。行为任务是条件性回避，刺激是带限噪声（500 - 1500赫兹）。在所有动物中，对于0至±200微秒的参考ITD，平均辨别阈值为50 - 60微秒。在这个参考ITD范围内，阈值没有趋势变化。对于±300微秒的参考ITD，这接近该物种头部宽度所定义的生理窗口极限，辨别阈值增加到约100微秒。兔子的ITD辨别能力不如头部大小相似的猫敏锐。这一结果支持了这样的观点，即ITD辨别能力，就像声音定位一样[见赫夫纳，1997年。《耳鼻咽喉头颈外科杂志》532（增刊），46 - 53页]，是由头部大小以外的因素决定的。
