Sensitivity in changing-loudness aftereffects as indicated by an adjustment procedure: implications regarding mechanisms.

The reduced sensitivity that accompanies some auditory aftereffects has been linked to sensory fatigue. However, changing-loudness aftereffects are unaffected by reduced sensitivity, according to previous evidence from a single-interval forced-choice procedure. That result was confirmed in the present study, in which an adjustment procedure was used to measure changing-loudness aftereffects. In each condition, the listener set the rate of intensity change in test stimuli until they were 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 changing intensity: The greater the standard deviation, the less the sensitivity. Consistent with previous data, the magnitude of increasing-loudness aftereffects (Experiment 1) and decreasing-loudness aftereffects (Experiment 2) varied according to the adaptation condition, but sensitivity did not. Although sensory fatigue may contribute to aftereffects, the author concluded that reduced sensitivity is not a reflection of sensory fatigue. Instead, it may be explained as a methodological artifact dependent on whether the adapted property is processed by direct or indirect mechanisms. Aftereffects only concern direct mechanisms, but the test stimuli used in their measurement may entail both types of mechanisms: If the measurement entails both types of mechanisms, sensitivity is reduced; if not, sensitivity is unaltered.