The scintillating grid illusion during smooth pursuit, stimulus motion, and brief exposure in humans

The Scintillating Grid Illusion occurs when small white disks are superimpo sed onto the intersections of a grey-on-black Hermann grid. As a result ill usory dark spots are seen at numerous crossings, flashing with each flick o f the eye and changing their location and distribution with each saccade. T he illusion is absent with steady fixation. The present study shows that sa ccadic eye movements are not necessary to produce the illusion. Rather, the illusion was also found to occur (i) during smooth pursuit movements when the grid was stationary, (ii) during smooth displacement of the grid with t he gaze kept steady, and (iii) during brief exposures of the stationary gri d. It is concluded that, while transient stimulation is essential for gener ating the illusion, reduction in effective luminance contrast resulting fro m brief exposure and high stimulus speed are responsible for reductions in its strength. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.