High- and Low-Frequency Loudness Adaptation

Abstract

Recent literature [Stockinger and Studebaker, (1968) and Petty, Fraser, and Elliott (1970)] contradicts much of the preexisting data concerning the magnitude and time course of suprathreshold loudness adaptation. A detailed study was undertaken to determine the magnitude of suprathreshold adaptation at 500 and 3000 Hz in six normal-hearing subjects. A controlled period of preadaptation was followed by 7 min of a continuous adapting signal of 70 dB SPL in one ear. The adapting tone was then continued an additional 4 min while a pulsed tone, identical to the pre-adapting conditions (3000 msec, 331/3% duty cycle, 10 msec rise-decay time) was introduced into the comparison ear for perstimulatory dichotic loudness balances. The experimental conditions were (1) adapting tone: 500 Hz; comparison tone: 400 or 3000 Hz; (2) adapting tone: 3000 Hz; comparison tone: 500 or 2000 Hz. Under these heterophonic conditions, adaptation was measured by the method of constant stimuli and repeated with a linear tracking technique. Essentially no adaptation was found at 500 Hz with either test method. At 3000 Hz a minimal decrement in loudness level (less than 5 dB) was obtained. The findings of minimal adaptation at 300 Hz and no adaptation at 500 Hz support the more recent literature indicating little, if any, loudness adaptation when binaural interaction is reduced or eliminated by a heterophonic procedure.