Concentrate for 30 seconds on the four vertical dots in the middle of the image.
Tip: It helps if you get as close to the screen as possible - but not so close that you can't see the four dots.

After staring at the four vertical dots, close your eyes and tilt your head back.
Keep them closed until you see a faint circle of light.
Keep staring at the circle... and then open your eyes.

What did you see?