Abstract
Purpose: Prolonged viewing of a moving stimulus results in illusory motion of a test stimulus in the opposite direction (MAE) and illusory slowing (motion fading, MF) of the adaptation stimulus. The two phenomena address different aspects of motion, but they might (or might not) be effects of the same underlying neural mechanisms. Here we studied this hypothesis. Methods: In 3 experiments, we compared MAE and MF directly with the same adaptation stimuli and the same observers. Magnitudes of MAE and MF for different adaptation durations, 1st and 2nd order stimuli, monocular and dichoptic presentation, and center/surround structure with high and low contrast were recorded. Results: MAE and MF size varied similarly as a function of adaptation duration and for 1st and 2nd order stimuli. Interocular transfer (IOT) for MAE was significantly smaller for 1st than 2nd order stimuli, but for MF, IOT was equivalent for both stimulus kinds. MAE was stronger for high than low contrast stimuli, but MF was better for low than high contrast stimuli. Conclusion: The results support the hypothesis that both phenomena do not arise from the same underlying neural mechanisms, and that MF is determined more by mechanisms at higher levels of processing.