SPECTRAL MOTION PRODUCES AN AUDITORY AFTER-EFFECT

DISTORTIONS of perception following prolonged exposure to an unvarying sensory stimulus have been observed since at least the third century BC1. The motion after-effect is a familiar experience2 in which, after a few minutes of viewing objects moving in a single direction, a stationary object appears to move in the opposite direction. Similar after-effects have been observed for many visual stimuli, including tilted lines, colours, stereoscopic depth, curvature, spatial frequency, contrast, rotation and motion in depth3-9. In contrast to the rich variety of visual after-effects reported since the 1960s, reports of analogous auditory adaptation effects only appeared in the 1970s10-12, but have continued since then13,14. Some effects of sound source spatial movement perception after adaptation to a spatially moving sound source have been reported15. Here we report an auditory perceptual after-effect analogous to the visual motion after-effect, which is caused by adaptation to auditory spectral (frequency) motion. After a few minutes of listening to a simple spectral pattern moving upwards or downwards in frequency space, the same pattern sounds as though it is drifting in the opposite direction when it is stationary. The effect shows binaural transfer, implying that it is generated at the level after binaural interaction. After-effects produced by the motion of spectral peaks are independent of those produced by spectral notches, suggesting separate processing channels for spectral peaks and notches.