Properties of Acoustic Reflex Adaptation

Abstract

The dynamic behavior of the acoustic reflex to continuous sinusoidal stimuli was investigated. The major purpose was to determine the temporal characteristics of reflex adaptation as frequency (0.5, 1.0, 2.0, 3.0, 4.0 kHz) and suprathreshold level (6, +12, +18 dB re reflex threshold) were systematically varied. Repeated measurements were made with an impedance bridge on six normal listeners. Both relative and absolute impedance changes were analyzed. The results revealed large intersubject variability. Four general conclusions were reached regarding the effect of stimulus frequency and suprathreshold level on adaptation: 1) as the stimulus frequency increases, the rate of adaptation increases; 2) the adaptation curves appear to form distinct groups, at the low frequencies adaptation rates are significantly slower than those at 2.0 kHz and above; 3) the onset of adaptation occurs at an earlier time for the higher frequencies; and 4) the rate of adaptation was found to be independent of suprathreshold level. The changes in adaptation with frequency of the stimulus may be expressed by an equation involving inter-related time constants for the growth and adaptation portions of the reflex curve in accordance with a descriptive model suggested by Tietze.