Gideon Caplovitz¹; ¹University of Nevada Reno

Radial gratings can induce all sorts of perceptual effects like Mackay's Chrysanthemum Rays or if you move your eyes: The Sunburst Illusion. If you rotate radial gratings on a computer monitor things get really weird with effects ranging from shape distortions, wagon-wheel type motion reversals and very strong spiraling motion after effects when they stop. I will demonstrate that when they stop rotating radial gratings also produce a novel dynamic illusion that manifests as a brief sequence of circular rings that rapidly expand from the near center out into the periphery, like the ripples produced by throwing a rock in a pond (but faster!) Even though the inducing stimulus is achromatic, this "discharge" is commonly reported as being yellowish but can appear in different hues to different observers. Like Laviant's Enigma or the Mackay Rays, the effect is disembodied from the inducing stimulus. Intriguingly, once experienced, some observers report seeing stationary chromatic rings superimposed on the radial grating even when it is not rotating, although we have not tested how long this effect lasts. In a series of experiments we document effects of radial and temporal frequency on the presence, hue and persistence of these ripples.