Optical illusions
Do you see the white dots at the crossings of the grid?
Fixate the dot in the centre. Now, try to move towards and away from your monitor!

Here are some examples how our vision can be misled through optical illusions. Try it yourself!

Here, you can find an extensive collection of optical illusions:

www.michaelbach.de/ot

www.kerstin-sell.de/illusionen