Fixate the colored image by looking at the fixation spot for about 60 seconds. Now shift your eyes to the fixation spot surrounded by rectangular outlines. If you attend to the vertical outline rectangle you will see the afterimage corresponding to it, and if you attend to the horizontal outline rectangle you will see the different afterimage corresponding to it. You can shift which afterimage you experience by attending to one rectangle and then the other.
(© 2010 Peter Tse)
VN:F [1.9.22_1171]Attention-biased after-image rivalry,