Illusion-Destruction by Appropriate Scaling

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Abstract
The inappropriate constancy scaling theory of visual distortion illusions is tested by optically projecting typical models giving these figures by perspective. Appropriate or inappropriate stereoscopic disparities are then added–with the prediction that when perspective and stereo are geometrically correct the distortion should vanish. This is confirmed with measurements for the Müller-Lyer illusion and by observation of several other classical examples. It is suggested that much previous work has investigated ‘end stop’ conditions, given by angles too extreme to be generated as perspective. Conditions for appropriate scaling, giving zero or small distortions, are found to be critical but readily attainable.