I read an article about a person at a museum who was looking around, and suddenly saw a picture floating in the room. When they looked back, the picture was gone.
It turns out the museum installed a device in the corner of the room that shows a single column of colored lights. The lights rapidly change to show each column of a picture, one-at-a-time, going from one side of the picture to the other. If you look at the device, it just appears to be a narrow bar of changing lights, but if your eye moves across the device, the complete image gets projected across the back of your eye.
I was intrigued by this, so I created a simple app to demonstrate the effect.
Hold your phone about a foot from your face, and watch one of the colored dots move back and forth. Keep your head still and just follow with your eyes. If you follow the green dot, the image points in one direction. If you follow the red dot, the image points in the other direction.
The animated gif below is a little too slow to work. You need to see it on a real iPhone.
