Perstimulatory fatigue, or adaptation, is measured by a simultaneous loudness balance or median plane localization of a dichotically presented acoustic stimulus. After one ear has been stimulated for a period of time, it is usually found that the variable or comparison stimulus must be reduced below the prefatiguing intensity in order to maintain the loudness match or localization balance.
Five observers made median plane localizations of a continuous 100–5000 cps band‐pass noise before, during and after a seven‐minute fatiguing period. The fatiguing stimuli were continuous noises at 30, 60, 87, and 100 db SPL, and noises interrupted at 1, 2, 5, 9, and 12.5 ips with both burst level and noise‐time fractions held constant at 90 db SPL and 0.5, respectively.
It was found that (a) the time required for fatigue to reach an apparent asymptote is at least seven minutes, about twice that required for pure tones; (b) the maximum fatigue increases with the intensity of the fatiguing stimulus and the function is positively accelerated; (c) for a fixed intensity of fatiguing noise, the maximum fatigue for the highest rate of interruption used (12.5 ips) is less than that obtained with a continuous noise having the same over‐all level (87 db).
During the course of fatigue, the between‐observer variations (standard deviations) of the balances tend to be greater than the within‐observer variations; the reverse is true for the post‐fatigue period.