Eye movements and decrement in the Oppel-Kundt illusion

Two groups of 15 Ss each observed the Oppel-Kundt illusion, in which a divided extent appears longer than an undivided extent. The group which made saccadic eye movements over the figure showed significant decrement of the illusion, while the group which maintained steady fixation showed no decrement. These results support an interpretation which maintains that information from eye-movement errors provides data as to the nature and extent of the illusion, thus leading to decrement.