An unreported size illusion.

A previously unreported size illusion in some commonly used stimuli--a large (global) letter made up of small (local) letters (eg a large H made up of small Es) is described: the size of the local letters forming the horizontal component of the global letter appears to be over-estimated. Global and local letters made up of horizontal and vertical components (E, F, T, and H) were employed as stimulus material. The first experiment showed that the illusion was consistently perceived, and was present for most of the stimuli tested; ie for all global letters and for all local letters except H. A second experiment showed that the size distortion is not specific to a particular dimension: instructing observers to focus on the height or the width of the local letters did not affect the extent of the illusion. The effect of some stimulus manipulations was also investigated.