Evidence for frequency-dependent and frequency-independent components in increasing- and decreasing-loudness...

Listening to a decreasingly intense tone leads to increasing loudness in a subsequent steady tone. Conversely, listening to an increasingly intense tone leads to decreasing loudness in a subsequent steady tone. Measurement entails a test stimulus changing in sound level to null any aftereffect, so that loudness is perceived as steady. Previous studies have shown that the aftereffects are frequency dependent: Carrier frequencies of adapting and test stimuli must be closely matched for the greatest aftereffects. In the present study, frequency-independent components were also indicated: Despite separation between adapting and test frequencies of up to two octaves, measurements always differed after decreasing and increasing sound-level adaptation, such that frequency functions for the two directions of adaptation never crossed. According to evidence from other negative adaptation effects in the auditory modality, explanation of the present aftereffects requires at least two mechanisms: Frequency-dependent components may reflect sensory processing, whereas frequency-independent components may be nonsensory in origin.