Ebbinghaus illusion

Ebbinghaus illusion

The Ebbinghaus illusion is an optical illusion of relative size perception. In the best-known version of the illusion, two circles of identical size are placed near to each other and one is surrounded by large circles while the other is surrounded by small circles; the first central circle then appears smaller than the second central circle.

It was named for its discoverer, the German psychologist Hermann Ebbinghaus (1850-1909).

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 Ebbinghaus illusion.

References

* Cite journal
author = V. H. Franz, F. Scharnowski and K. R. Gegenfurtner
year = 2005
title = Illusion effects on grasping are temporally constant not dynamic
journal = J Exp Psychol Hum Percept Perform
volume = 31
issue = 6
pages = 1359–1378
url = http://www.allpsych.uni-giessen.de/karl/pdf/51.dynamo.pdf
doi = 10.1037/0096-1523.31.6.1359
* Cite journal
author = M. A. Goodale & David Milner
year = 1992
title = Separate pathways for perception and action
journal = Trends in Neuroscience
volume = 15
issue = 1
pages = 20–25
month = January
pmid = 1374953
doi = 10.1016/0166-2236(92)90344-8


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