4pPP1. Acoustic reflex decay for modulated signals.

Session: Thursday Afternoon, May 16

Author: Raymond D. Cook
Author: Michael O. Ferguson
Author: Joseph W. Hall III
Author: John H. Grose
Author: Harold C. Pillsbury
Location: Div. of Otolaryngol., Head and Neck Surgery, Univ. of North Carolina, 610 Burnett-Womack, CB# 7070 Chapel Hill, NC 27599


Temporal decay of the acoustic reflex provides the basis for an objective audiological test that differentiates cochlear from retrocochlear pathologies. The classic sign of a neural lesion is a rapid decay of the reflex under conditions of pure-tone stimulation for frequencies 1000 Hz and below. This restriction to lower frequencies is due to the fact that even normal ears show decay for higher-frequency signals. At present, it is unclear whether the acoustic reflex decay (ARD) seen in normal ears is related to frequency-specific channels or whether the critical variable is the timing information coded within the channels. This study examined ARD in subjects with normal hearing and middle ear function. The degree of ARD was measured for both modulated and unmodulated carrier frequencies of 500, 1000, 2000, and 4000 Hz with modulation rates of 50 -- 400 Hz. The dependent variable was the half-life of the decaying reflex (ARD 50%) over a 12-s stimulation interval. Significant ARD was present for high-frequency unmodulated carriers, but not for low-frequency carriers. For all listeners, ARD was diminished for all modulated stimuli, suggesting that resistance to ARD is mediated by the temporal characteristics of the stimulus. [Work supported by the American Hearing Research Foundation.]

from ASA 131st Meeting, Indianapolis, May 1996