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Abstract:
Several reports in the literature indicate that visual size illusions may not have an influence on visually guided hand movements, i.e. that movement planning may not be subject to the illusion, implying that there exist two at least partly separated systems. One of these should deal with "pure" perception, the other one with "perception for action". We tested the effect of the Ebbinghaus size illusion on both perception and grasping. An "isolated" form of the illusion (either a large circle among small circles OR vice versa) produced virtually identical results for grasping and perception, while a "simultaneous" version had a larger influence on perception than on grasping. The results cast some doubts on conventional ways to demonstrate the separation of pathways in normal subjects.
