Found in virtually every psychology textbook in the world, the two monsters in this illusion are in fact the same size. Your brain automatically adjusts images that it perceives to be distant in order to compensate for the fact that they are larger than they seem.
Named after Robert Jastrow in 1889, the bottom figure appears to be larger although they are both the same size. This is because the shorter edge of “A” is directly adjacent to the longer edge of “B”.
First described by British psychologist James Fraser in 1908, this illusion is also known as the “false spiral”. While it appears that the overlapping arcs are spiralling into infinity they are in fact only a series of concentric circles.
This is a variation of the Hermann Grid where black dots appear and disappear at the intersections of the gray lines. Interestingly enough, if you cock your head at a 45 degree angle the effect is reduced (but not eliminated).
There are several variations to this illusion but the effect is the same. The “blue” and “green” backgrounds are in fact the same color (open it in photoshop).