Just FYI to anyone thinking of doing this: &quot;prolonged time&quot; can mean <i>years</i>. For me, the effect is still there even if very faint. I see the green and red, just initially whenever I view the checkerboard, and it goes away after a few seconds. I did the exercise I think probably sometime in 2010.<p>Although I am happy to report that the impact on other areas of my life has been zero, as far as I know.