ABSTRACT
John Clavadetscher’s thesis is a landmark in illusion theory. It provides the first effective formulation that allows joint operation of the two basic processes commonly called assimilation and contrast. Although the existence of these two processes was apparent in the earliest studies a century ago, demonstrating their joint operation is surprisingly difficult. The U-shaped curve ingeniously conjectured and verified by Clavadetscher is a triumph, therefore, because it clearly demonstrates joint operation of the two processes in the Ebbinghaus-Titchener circles illusion.
