Some Properties of the Acoustic Reflex in Man

Abstract

This paper describes instrumentation and a technique for measurement of both static acoustic impedance and changes in complex acoustic impedance at the tympanic membrane. White noise was used to activate the acoustic reflex. Five subjects were exposed to this noise at levels between 50 and 110 dB SPL (over all) and with durations between 5 msec and 10 min. Changes in acoustic impedance were recorded at the subject's right ear while the noise was presented to his left. At some noise levels, the acoustic reflex was sustained for at least 10 min. The latency and strength of the reflex, and its adaptation, all were related to the level of the noise. Time required for a maximum change in acoustic impedance was related inversely to noise level. Pulsed noise was more effective than steady noise in eliciting the reflex. The acoustic reflex was observed, on the average, at an over-all SPL of 69 dB for steady noise and 63 dB for pulsed noise. [Work supported by program, project grant B-3856 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health. U. S. Department of Health, Education, and Welfare.]