Similarity and lightness effects in Ebbinghaus illusion created by keyboard characters

36 observers judged the size of a central S in variants of the Ebbinghaus f igure having contextual Ss, $s, or Hs. When the figures were composed of si milarly shaped elements. underestimation of the central S was obtained. Man ipulations of lightness indicated that these underestimations were stronges t for figures with gray contextual characters and a black central S and wea kest for figures with black contextual characters and a gray central S. All black or all gray figures produced intermediate illusions. The data are co nsistent with Choplin and Medin's 1995, claim that figural properties rathe r than semantic similarity influences size contrast and further show that t he visual processes underlying size contrast include interactions of contou rs.