Computation of mean size is based on perceived size
The present study investigated whether computation of mean object size was based on perceived or physical
size. The Ebbinghaus illusion was used to make the perceived size of a circle different from its physical size.
Four Ebbinghaus configurations were presented either simultaneously (Experiment 1) or sequentially (Experiment 2) to each visual field, and participants were instructed to attend only to the central circles of each configuration. Participants’ judgments of mean central circle size were influenced by the Ebbinghaus illusion. In
addition, the Ebbinghaus illusion influenced the coding of individual size rather than the averaging. These results
suggest that perceived rather than physical size was used in computing the mean size.
Im, H.Y., & Chong, S.C.(2009). Computation of mean size is based on perceived size. Attention, Perception, & Psychophysics,71, 375-384 [PDF]