Dynamics of the Acoustic Reflex: Phenomenological Aspects

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Abstract
The acoustic reflex was studied by measuring the variations in the mechanical-input impedance to the ears of 6 normal human subjects. The auditory system was stimulated by wide-band noise at various intensity levels. Static magnitude and phase characteristics of the response were obtained at several frequencies. Reflex activity results in an increase in the magnitude and a decrease in the phase lag of the ear''s input-impedance. The system dynamics were studied with step stimuli. At stimulus onset both the latency and speed of the response are related to stimulus magnitude. With higher intensities, shorter latency and faster response results. At cessation of the stimulus, there was no clear functional relationship between latency and intensity. For some subjects, faster reflex relaxation occurred after low-intensity stimulation than after more-intense activity; for other subjects, there was no such clear trend. It was observed that, during prolonged stimulation with very high-intensity noise, stable reflex activity resulted; but if the stimulus was weaker, then response adaptation occurred. In the vicinity of reflex threshold, the adaptation was usually quite rapid.

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