ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aPP4. Directionality of sound-pressure transformation at the pinna of Mus domesticus.

Qi-Cai Chen

Dept. of Biology, Central China Normal Univ., Wuhan, Hubei, People's Republic of China

David Cain

Philip H.-S. Jen

Univ. of Missouri, Columbia, MO 65211

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 of 10--80 kHz tested. 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 (i.e., the negative pressure). 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. 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. [Work supported by NIH and HFSP.]