Keller C H, Hartung K, Takahashi T T
Institute of Neuroscience, University of Oregon, Eugene 97403, USA.
Hear Res. 1998 Apr;118(1-2):13-34. doi: 10.1016/s0378-5955(98)00014-8.
Sounds arriving at the eardrum are filtered by the external ear and associated structures in a frequency and direction specific manner. When convolved with the appropriate filters and presented to human listeners through headphones, broadband noises can be precisely localized to the corresponding position outside of the head (reviewed in Blauert, 1997). Such a 'virtual auditory space' can be a potentially powerful tool for neurophysiological and behavioral work in other species as well. We are developing a virtual auditory space for the barn owl, Tyto alba, a highly successful auditory predator that has become a well-established model for hearing research. We recorded catalogues of head-related transfer functions (HRTFs) from the frontal hemisphere of 12 barn owls and compared virtual and free sound fields acoustically and by their evoked neuronal responses. The inner ca. 1 cm of the ear canal was found to contribute little to the directionality of the HRTFs. HRTFs were recorded by inserting probetube microphones to within about 1 or 2 mm of the eardrum. We recorded HRTFs at frequencies between 2 and 11 kHz, which includes the frequencies most useful to the owl for sound localization (3-9 kHz; Konishi, 1973). Spectra of virtual sounds were within +/- 1 dB of amplitude and +/- 10 degrees of phase of the spectra of free field sounds measured near to the eardrum. The spatial pattern of responses obtained from neurons in the inferior colliculus were almost indistinguishable in response to virtual and to free field stimulation.
到达鼓膜的声音会被外耳及相关结构以频率和方向特异性的方式进行过滤。当与适当的滤波器进行卷积，并通过耳机呈现给人类听众时，宽带噪声可以被精确地定位到头部外部的相应位置（Blauert，1997年综述）。这样一个“虚拟听觉空间”对于其他物种的神经生理学和行为学研究也可能是一个强大的工具。我们正在为仓鸮（Tyto alba）开发一个虚拟听觉空间，仓鸮是一种非常成功的听觉捕食者，已成为听觉研究的成熟模型。我们记录了12只仓鸮额叶半球的头部相关传递函数（HRTF）目录，并通过声学和诱发神经元反应比较了虚拟声场和自由声场。发现耳道内约1厘米的部分对HRTF的方向性贡献很小。通过将探针式麦克风插入到距鼓膜约1或2毫米的位置来记录HRTF。我们在2至11千赫的频率范围内记录了HRTF，其中包括对猫头鹰声音定位最有用的频率（3至9千赫；Konishi，1973年）。虚拟声音的频谱在鼓膜附近测量的自由场声音频谱的幅度±1分贝和相位±10度范围内。在下丘神经元获得的反应空间模式在对虚拟刺激和自由场刺激的反应中几乎无法区分。
