Perstimulatory Fatigue as Measured by Heterophonic Loudness Balances

Perstimulatory fatigue is the decrease in loudness of a steady auditory stimulus during its presentation. In the past it has been measured by requiring a simultaneous dichotic loudness balance between two pure tones, one in each ear. Under these conditions the listener hears a single phantom sound whose localization depends upon the relative intensities of the two tones. The present investigation shows that the process of localizing the sound image in making the loudness balance is not critical to the occurrence of perstimulatory fatigue. Two principal conditions were compared. In the first, the frequency of the comparison stimulus was the same as that of the fatiguing stimulus. In the second, the comparison and fatiguing stimuli differed sufficiently in frequency (cps) so that the listener always could correctly localize the two tones. The amount of perstimulatory fatigue is the same under these two conditions. A procedure is developed which largely prevents the constant errors that result from the formation of a single absolute standard of loudness. This method results in greater measured fatigue than the usual procedure. This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, Air Research and Development Command.