Acoustic reflex decay for pulse train signals

Abstract

Currently, the acoustic reflex decay (ARD) test is useful in testing for auditory nerve tumors, but only at low frequencies, as even normal-hearing subjects show ARD to pure tones at frequencies higher than 1000 Hz. The purpose of this study is to develop a reliable high-frequency test of ARD and to achieve a better understanding of the mechanism underlying ARD. ARD was measured in eighteen normal-hearing subjects using pulse trains with rates of 50, 100, 200, 400, and 800 Hz. Each of these pulse trains was then bandpass filtered with a fixed high-pass setting of 4.5 kHz, and a variable low-pass setting of 5, 6, 8, or 10 kHz. In addition, random noise filtered to similar bandwidths was also tested. Results suggest that the acoustic reflex is resistant to decay for high-frequency pulse train stimuli with rates of 200 Hz and below, whereas rates of 400 Hz and above, as well as high-pass filtered noise, result in significant decay. There seems to be little effect of stimulus bandwidth. These data indicate a strong temporal component to acoustic reflex decay. [Work supported by the American Hearing Research Foundation.]