What to see Below you see a rotating array of blue crosses
and 3 yellow dots. Now fixate on the centre (watch the flashing green
spot). Note that the yellow spots disappear once in a while: singly, in
pairs or all three simultaneously. In reality, the 3 yellow spots are
continuously present, honest!
What to do You can use the slower/faster buttons to change
speed. Disappearance persists down to surprisingly low speeds. [If there
are no buttons on the right, please update your Flash player.]
You can use the larger/smaller buttons to change size. Disappearance persists up to surprisingly large sizes.
You can use the “back-col” button to change the background colour. The yellow dots disappear into whatever colour the background has.
The ‘defaults’ button at the top restores the standard settings.
Comment According to Michael Bach, "Steady fixation favours disappearance, blinks or gaze
shifts induce reappearance. All in all reminiscent of the Troxler effect, but stronger and
more resistant to residual eye movements."
Source This page provided by Prof. Michael Bach PhD, Ophthalmology, University of Freiburg, Germany, from his collection of Optical Illusions & Visual Phenomena.