LOUDNESS ADAPTATION AT HIGH-FREQUENCIES

Loudness adaptation was measured for pure tones at 4, 12, 14, and 16 kHz. In three experiments, a total of 87 young listeners judged-by the method of successive magnitude estimation-the loudness of the tones over a 6-min exposure period. Thresholds were measured by an adaptive 21FC procedure. Although earlier measurements had shown that adaptation near threshold increases with frequency, these new data reveal that the increase is especially marked at higher sensation levels. Thus, at 40 dB SL, over a 6-min period loudness declined by 18% at 4 kHz and by 94% at 16 kHz. Moreover, the 4-kHz tone remained audible for all listeners throughout the 6-min exposure period whereas the 16-kHz tone became inaudible for two-thirds of them by the end of the exposure period. Listeners with relatively low thresholds (< 50 dB SPL) at 16 kHz showed much less adaptation at 14 kHz than at 16 kHz and much less than listeners with relatively high thresholds (> 50 dB SPL) at 16 kHz; this latter group showed strong adaptation at 14 kHz. The marked loudness adaptation of steady tones at very high frequencies and relatively high sensation levels is associated with a restricted spread of excitation in the auditory system resulting from the steep rise of the threshold curve at the highest audible frequencies.