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Ebbinghaus Illusion




It was named for its discoverer, Hermann Ebbinghaus .

The Ebbinghaus illusion has played a crucial role in the recent debate over the existence of separate pathways in the brain for perception and action (for more details see Visual Cortex ). It has been argued that the Ebbinghaus illusion distorts ''perception'' of size, but when a subject is required to respond with an ''action'', such as grasping, no size distortion occurs (Goodale & Milner, 1992). However, recent work (Franz ''et al'', 2005) suggests that the original experiments were flawed. The original stimuli limited the possibility for error in the grasping action, therefore making the grasp response more accurate, and presented the large and small versions of the stimulus in isolation - which results in ''no illusion'' because there is no second central circle to act as a reference. Franz ''et al'' conclude that both the action and perception systems are equally fooled by the Ebbinhaus illusion.


References

  • Franz VH, Scharnowski F, Gegenfurtner (2005) Illusion effects on grasping are temporally constant not dynamic. J Exp Psychol Hum Percept Perform. 31(6), 1359-78

  • Goodale & Milner (1992) Separate pathways for perception and action. Trends in Neuroscience, 15, 20-25.