4pPP12. Acoustic properties of the chinchilla pinna and ear canal.

Session: Thursday Afternoon, May 16

Author: William J. Murphy
Author: Rickie R. Davis
Location: Bioacoust. and Occup. Vib. Sect., Natl. Inst. for Occup. Safety and Health, MS C-27, 4676 Columbia Pkwy., Cincinnati, OH 45226-1998


Measurements of the acoustic transfer function (ATF) of the pinnae of 4 chinchillas were compared with the auditory-evoked potential (AEP) hearing thresholds of 16 chinchillas measured in free field and with insert earphones. The ATF was measured in anesthetized chinchillas in a far-field condition in a semi-anechoic room. Probe microphone measurements were collected just outside the pinna and at the tympanic membrane. The ATF exhibited a broad resonance between 2 and 6 kHz with about a 10 dB gain. The chinchillas were monauralized and had a chronic electrode implanted in the left inferior colliculus. The animals were awake and restrained during the AEP testing. The AEP measurements were averaged from 512 presentations of a toneburst at 0.5, 1, 2, 4, and 8 kHz. AEPs collected with insert earphones were calibrated with a probe microphone positioned near the tympanic membrane. The differences in the AEP hearing thresholds measured in the different configurations exhibited a 10 dB resonance at 4 kHz. The agreement between the ATF and AEP-derived transfer function suggested that the threshold differences from the two testing configurations could be accounted for by the pinna and ear canal gain.

from ASA 131st Meeting, Indianapolis, May 1996