The configuration of lizard ears, where sound can reach both surfaces of the eardrums, produces a strongly directional ear, but the subsequent processing of sound direction by the auditory pathway is unknown. We report here on directional responses from the first stage, the auditory nerve. We used laser vibrometry to measure eardrum responses in Tokay geckos, and in the same animals recorded 117 auditory nerve single fiber responses to free-field sound from radially distributed speakers. Responses from all fibers showed strongly lateralized activity at all frequencies, with an ovoidal directivity that resembled the eardrum directivity. Geckos are vocal and showed pronounced nerve fiber directionality to components of the call. To estimate the accuracy with which a gecko could discriminate between sound sources, we computed the Fisher information (FI) for each neuron. FI was highest just contralateral to the midline, front and back. Thus, the auditory nerve could provide a population code for sound source direction, and geckos should have a high capacity to differentiate between midline sound sources. In brain, binaural comparisons, for example by IE neurons, should sharpen the lateralized responses and extend the dynamic range of directionality.

中文翻译：

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对 Tokay 壁虎 Gekko 壁虎听觉神经中的音调和特定呼叫的强烈定向反应。

蜥蜴耳朵的结构，声音可以到达鼓膜的两个表面，产生一个方向性很强的耳朵，但听觉通路对声音方向的后续处理是未知的。我们在这里报告来自第一阶段的定向反应，即听觉神经。我们使用激光测振法来测量 Tokay 壁虎的耳膜反应，并在相同的动物中记录了 117 个听觉神经单纤维对来自径向分布的扬声器的自由场声音的反应。所有纤维的反应在所有频率都显示出强烈的侧向活动，具有类似于鼓膜方向性的卵形方向性。壁虎是发声的，并且对呼叫的组成部分表现出明显的神经纤维方向性。为了估计壁虎区分声源的准确度，我们计算了每个神经元的 Fisher 信息 (FI)。FI 在中线、前后对侧最高。因此，听觉神经可以提供声源方向的种群代码，壁虎应该具有区分中线声源的高能力。在大脑中，双耳比较，例如通过 IE 神经元，应该加强侧向反应并扩展方向性的动态范围。