Ponzo illusion stimulus and Ebbinghuas illusion stimulus. In the Ponzo illusion (A, B), the two converging lines provided the depth impression that the two physically identical objects were located at different distances from the observer, and the distant object looks larger than the object that appears closer in space. In the Ebbinghaus illusion (C), the object surrounded by small items looks larger than a physically identical object surrounded by big items.
Song et al. BMC Neuroscience 2011 12:27 doi:10.1186/1471-2202-12-27