Increasing- and decreasing-loudness aftereffects: asymmetrical functions for absolute rate of sound level change in adapting stimulus.

After exposure to a tone of decreasing sound level, participants report that a steady tone increases in loudness; after exposure to an increasing sound level, they perceive a steady tone to decrease in loudness. The increasing-loudness aftereffect is the more sensitive to a difference between adapting and test frequencies, its absolute size becoming greater than that for decreasing-loudness aftereffect as frequencies are made to match. Although this asymmetry may reflect processing differences for the two directions of sound level change, a more parsimonious hypothesis entails perceived increasing loudness of short steady tones, in conjunction with differing levels of tonal adaptation across test frequencies. The former explanation is supported by the present report of another aftereffect asymmetry: With frequency the same for both adapting and test stimuli, so that tonal adaptation was nearly asymptotic during testing, altering the absolute rate of sound level change of the adapting stimulus had a greater effect on the magnitude of the increasing-loudness aftereffect. The first hypothesis is consistent with the percussive nature of natural sounds, few of which are steady: most of their sound levels rise almost instantaneously and decrease slowly.