(© 2006 Alan Stubbs)

For the primary effect, one should sit at a comfortable distance and then move forward toward the center of the figure. An interesting change in apparent brightness and to some degree form will result—what may be called a “here comes the sun” effect. By moving back and forth, this apparent change will repeat.

See different versions of the illusion

Read more about the illusion and possible explanations

A new set of illusionsthe Dynamic Luminance-Gradient Illusion and the Breathing Light Illusion Simone Gori & D. Alan Stubbs Perception. 2006. 35:1573-7

(© 2005 Peter U. Tse)

Attention-induced brightness changes occur over bistable transparent surfaces. Fixate any of the points above and shift your attention to one disk or other without moving your eyes. The attended disk appears to change brightness. We believe that this happens because attention biases figure formation such that filling-in happens differently within the attended region than in the unattended region. In particular, the features from the overlap region spread within the boundaries of the attended figure, and not within the boundaries of the unattended region. This happens only for bistable transparent surfaces because only then is it ambiguous over which surface or layer the visual system should carry out the filling-in operation.

Read more about the illusion and possible explanations

Voluntary attention modulates the brightness of overlapping transparent surfaces Peter U. Tse Vision Research. 2005. 45:1095-8