SENSITIVITY IN CHANGING-LOUDNESS AFTEREFFECTS AS INDICATED BY AN ADJUSTMENT PROCEDURE - IMPLICATIONS REGARDING MECHANISMS

The reduced sensitivity that accompanies some auditory aftereffects ha s been linked to sensory fatigue. However, changing-loudness aftereffe cts are unaffected by reduced sensitivity, according to previous evide nce from a single-interval forced-choice procedure. That result was co nfirmed in the present study, in which an adjustment procedure was use d to measure changing-loudness aftereffects. In each condition, the li stener set the rate of intensity change in test stimuli until they wer e heard as steady in loudness. The mean of 10 such settings was taken as a measure of the aftereffect's magnitude. The standard deviation of the 10 settings indicated the listener's sensitivity in perceiving ch anging intensity: The greater the standard deviation, the less the sen sitivity. Consistent with previous data, the magnitude of increasing-l oudness aftereffects (Experiment 1) and decreasing-loudness aftereffec ts (Experiment 2) varied according to the adaptation condition, but se nsitivity did not. Although sensory fatigue may contribute to aftereff ects, the author concluded that reduced sensitivity is not a reflectio n of sensory fatigue. Instead, it may be explained as a methodological artifact dependent on whether the adapted property is processed by di rect or indirect mechanisms. Aftereffects only concern direct mechanis ms, but the test stimuli used in their measurement may entail both typ es of mechanisms. If the measurement entails both types of mechanisms, sensitivity is reduced; if not, sensitivity is unaltered.