Response scatter in measuring changing-loudness aftereffects: Evidence for simplified processing of auditory motion-in-depth and potential collision

Researchers have postulated 2 mechanisms for processing auditory motion: a direct mechanism processing motion itself and an indirect mechanism sensitive to location over discrete points in time. Measuring aftereffects of azimuthal motion by nulling entails scattered responding, which is attributed to a conflict between direct and indirect mechanisms. In this experiment, the author obtained nulls following adaptation to changing sound level, a property of approaching or receding sound sources, and for nonadaptation. Test stimuli ranged in duration from 1.0 to 2.5 s. Longer test stimuli evinced reductions in both changing-loudness aftereffects and the associated response scatters. However, the latter matched the nonadaptation response scatters. The author suggests that judging longer test stimuli is easier, so an indirect mechanism need not be invoked. Simplified processing of changing sound level may underlie the rapid responses required for potential collision.