To begin, you’ll need to fixate the coloured image (one on your left) by looking at the fixation spot for about 60 seconds. Now shift your eyes to right hand box. Which afterimage did you see first? You can manually shift which afterimage you experience by attending to one rectangle and then the other. 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. Now wasn’t that great?!