Chen Q C, Cain D, Jen P H
Division of Biological Sciences, University of Missouri-Columbia 65211, USA.
J Exp Biol. 1995 Sep;198(Pt 9):2007-23. doi: 10.1242/jeb.198.9.2007.
Sound pressure transformation properties at the pinna of laboratory mice Mus domesticus were studied by measuring the sound pressure level of a continuous tone at a series of frequencies at the tympanic membrane as a function of the position of a sound source under free-field stimulation conditions. The spectral transformation, the interaural spectral difference, the isopressure contours and the interaural pressure difference contours were plotted. Sound pressure transformation functions showed some prominent spectral notches throughout the frequency range tested (10-80 kHz). However, the notch frequency did not appear to be systematically related to sound direction. The study of interaural pressure difference demonstrated that, when delivered from some angles within the ipsilateral frontal hemisphere, the sound pressure at the tympanic membrane of certain frequencies may be lower than that determined at the corresponding contralateral angles. For each sound frequency tested, there was an angle (the acoustic axis) within the ipsilateral frontal hemisphere from which the delivered sound reached a maximal pressure level at the tympanic membrane. However, the acoustic axis often changed to a new angle after removal of the ipsilateral pinna. In addition, sound delivered from the acoustic axis did not always generate a maximal pressure transformation. The isopressure contours determined within 2-5 dB of the maximal pressure were circumscribed, and their contained angular areas were found to decrease with increasing sound frequency. The 2 dB maximal pressure area may appear at more than one angular area for some test frequencies. Removal of the ipsilateral pinna or modification of pinna posture expanded isopressure contours irregularly and split the 2 dB maximal pressure area into several parts. The sound pressure difference determined between the angles of maximal and minimal sound pressure (the maximal directionality) increased with sound frequency regardless of pinna posture. Acoustic gain of the pinna at the acoustic axis reached 6-12 dB, depending upon sound frequency. However, the pinna gain was not always maximal at the acoustic axis for a given frequency.
通过在自由场刺激条件下，测量一系列频率的连续纯音在鼓膜处的声压级，作为声源位置的函数，研究了实验小鼠（小家鼠）耳廓处的声压转换特性。绘制了频谱转换、双耳频谱差异、等压轮廓和双耳压差轮廓。声压转换函数在测试的整个频率范围（10 - 80 kHz）内显示出一些明显的频谱凹陷。然而，凹陷频率似乎与声音方向没有系统的关联。双耳压差的研究表明，当从同侧额叶半球内的某些角度传递声音时，特定频率在鼓膜处的声压可能低于在相应对侧角度处测得的声压。对于每个测试的声音频率，在同侧额叶半球内都有一个角度（声轴），从该角度传递的声音在鼓膜处达到最大压力水平。然而，去除同侧耳廓后，声轴常常会改变到一个新的角度。此外，从声轴传递的声音并不总是产生最大的压力转换。在最大压力的2 - 5 dB范围内确定的等压轮廓是受限的，并且发现它们所包含的角度区域随着声音频率的增加而减小。对于某些测试频率，2 dB最大压力区域可能出现在多个角度区域。去除同侧耳廓或改变耳廓姿势会不规则地扩大等压轮廓，并将2 dB最大压力区域分成几个部分。无论耳廓姿势如何，最大和最小声压角度之间确定的声压差（最大方向性）都随着声音频率的增加而增加。耳廓在声轴处的声增益达到6 - 12 dB，这取决于声音频率。然而，对于给定频率，耳廓增益并不总是在声轴处最大。
