Disparity (binocular) and the thumb experiment

Isn’t it surprisingly, how easy it can be to experiment with human perception without any tools? Here is a very simple one for binocular disparity.

Because of the space between our two eyes we perceives two distinct images. The difference of the images on our retinas can be easily recognized with the thumb experiment: You only have to put forth your hand, thumbs up. Now, if you first close the right eye and then the left one, the thumb seems to be at different places in comparison to the background (see Figure).

The very popular stereograms were formerly used for experiments on disparity. You stare at two distinctive images that have a relatively small distance from your eyes and try to look through them. When you have finally reached a rigid view, you get a 3D effect. You thereby switch off the convergence of the eyes.