Saberi K, Farahbod H, Konishi M
Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):6465-8. doi: 10.1073/pnas.95.11.6465.
Owls and other animals, including humans, use the difference in arrival time of sounds between the ears to determine the direction of a sound source in the horizontal plane. When an interaural time difference (ITD) is conveyed by a narrowband signal such as a tone, human beings may fail to derive the direction represented by that ITD. This is because they cannot distinguish the true ITD contained in the signal from its phase equivalents that are ITD +/- nT, where T is the period of the stimulus tone and n is an integer. This uncertainty is called phase-ambiguity. All ITD-sensitive neurons in birds and mammals respond to an ITD and its phase equivalents when the ITD is contained in narrowband signals. It is not known, however, if these animals show phase-ambiguity in the localization of narrowband signals. The present work shows that barn owls (Tyto alba) experience phase-ambiguity in the localization of tones delivered by earphones. We used sound-induced head-turning responses to measure the sound-source directions perceived by two owls. In both owls, head-turning angles varied as a sinusoidal function of ITD. One owl always pointed to the direction represented by the smaller of the two ITDs, whereas a second owl always chose the direction represented by the larger ITD (i.e., ITD - T).
猫头鹰和包括人类在内的其他动物，利用声音到达双耳的时间差异来确定水平面上声源的方向。当耳间时间差（ITD）由诸如纯音之类的窄带信号传递时，人类可能无法得出该ITD所代表的方向。这是因为他们无法将信号中包含的真实ITD与其相位等效值区分开来，这些相位等效值为ITD +/- nT，其中T是刺激纯音的周期，n是整数。这种不确定性称为相位模糊。当ITD包含在窄带信号中时，鸟类和哺乳动物中所有对ITD敏感的神经元都会对ITD及其相位等效值做出反应。然而，尚不清楚这些动物在窄带信号定位中是否表现出相位模糊。目前的研究表明，仓鸮（Tyto alba）在耳机发出的纯音定位中会经历相位模糊。我们使用声音诱发的转头反应来测量两只猫头鹰感知到的声源方向。在这两只猫头鹰中，转头角度均随ITD呈正弦函数变化。一只猫头鹰总是指向两个ITD中较小值所代表的方向，而另一只猫头鹰总是选择较大ITD（即ITD - T）所代表的方向。
