Coles R B, Guppy A
Research School of Biological Sciences, Australian National University, Canberra.
J Comp Physiol A. 1988 May;163(1):117-33. doi: 10.1007/BF00612002.
The acoustical properties of the external ear of the barn owl (Tyto alba) were studied by measuring sound pressure in the ear canal and outer ear cavity. Under normal conditions, pressure amplification by the external ear reaches about 20 dB between 3-9 kHz but decreases sharply above 10 kHz. The acoustic gain curve of the outer ear cavity alone is close to that of a finite-length exponential horn between 1.2-13 kHz with maximum gain reaching 20 dB between 5-9 kHz. Pressure gain by the facial ruff produces a maximum of 12 dB between 5-8 kHz and decreases rapidly above 9 kHz. The directional sensitivity of the external ear was obtained from pressure measurements in the ear canal. Directivity of the major lobe is explained, to a first approximation, by the sound diffraction properties of a circular aperture. Aperture size is based on the average radius (30 mm) of the open face of the ruff. Above 5 kHz, the external ear becomes highly directional and there is a 26 degree disparity in elevation between the acoustic axis of the left and right ear. In azimuth, directivity patterns are relocated closer to the midline as frequency increases and the acoustic axis moves at a rate of 20 degree/octave between 2-13 kHz. Movement of the axis can be explained, to a first approximation, by the acoustical diffraction properties of an obliquely truncated horn, due to the asymmetrical shape of the outer ear cavity. The directional sensitivity of the barn owl ear was studied by recording cochlear microphonic (CM) potentials from the round window membrane. Between 3-9 kHz, CM directivity patterns are clearly different to the directivity patterns of the external ear; CM directionality is abruptly lost above 10 kHz. Above 5 kHz, CM directivity patterns are characterized by an elongated major lobe containing the CM axis, forming a tilted band of high amplitude but low directionality (CM axial plane), closely bordered by minima or nulls. The highest directionality is found in the CM directional plane, approximately perpendicular to the CM axial plane. The left and right ear axial planes are symmetrical about the interaural midline (tilted 12 degrees to the right of the midline of the head) and inclined by an average of 60 degrees to the left and right respectively. In azimuth, the CM axis moves towards the midline at a rate of 37 degrees/octave as frequency increases from 2-9 kHz, crossing into contralateral space near 7 kHz.(ABSTRACT TRUNCATED AT 400 WORDS)
通过测量仓鸮（Tyto alba）耳道和外耳腔中的声压，研究了其外耳的声学特性。在正常情况下，外耳的压力放大在3至9千赫兹之间达到约20分贝，但在10千赫兹以上急剧下降。仅外耳腔的声学增益曲线在1.2至13千赫兹之间接近有限长度指数喇叭的曲线，在5至9千赫兹之间最大增益达到20分贝。面部羽领产生的压力增益在5至8千赫兹之间最大为12分贝，在9千赫兹以上迅速下降。外耳的方向敏感性是通过测量耳道中的压力获得的。主瓣的方向性，初步近似地，由圆形孔径的声音衍射特性来解释。孔径大小基于羽领开口面的平均半径（30毫米）。在5千赫兹以上，外耳变得高度定向，左耳和右耳的声轴在仰角上有26度的差异。在方位上，随着频率增加，方向性图案向中线靠近，并且声轴在2至13千赫兹之间以20度/倍频程的速率移动。声轴的移动，初步近似地，可以由斜截喇叭的声学衍射特性来解释，这是由于外耳腔的不对称形状。通过记录圆窗膜的耳蜗微音器（CM）电位，研究了仓鸮耳朵的方向敏感性。在3至9千赫兹之间，CM方向性图案与外耳的方向性图案明显不同；在10千赫兹以上，CM方向性突然消失。在5千赫兹以上，CM方向性图案的特征是包含CM轴的拉长主瓣，形成一个高幅度但低方向性的倾斜带（CM轴向平面），其紧邻最小值或零点。最高的方向性出现在CM方向平面中，大致垂直于CM轴向平面。左耳和右耳的轴向平面关于双耳中线对称（向头部中线右侧倾斜12度），并且分别向左和向右平均倾斜60度。在方位上，随着频率从2至9千赫兹增加，CM轴以37度/倍频程的速率向中线移动，在7千赫兹附近进入对侧空间。（摘要截断于400字）
