Optical illusion posters.

Optical Illusion posters. In Fig.1 (a), the length of the brim of the hat is the same as the height of the hat. In Fig.1 (b), the lower right hand slanted line 1, if extended, will intersect the left-hand line 0 where it joins the vertical. However, slanted line 2 actually looks like the one that will intersect with line 0. In Fig.2, the perfect circle appears distorted. In Fig.3 (a), the two diagonal lines are the same length. In Fig.3 (b), the two vertical lines are parallel and straight. These are all 'optical illusions with lines and angles'. In Fig.4 a flight of stairs is seen from above looking down, or from below looking up. This is an 'equivocal figure illusion'. In Fig.5, small gray spots are seen at the intersections of the white lines. The white lines look brighter against the black background, and the place where the white lines intersect seems less bright (or gray) in contrast with the white lines. If you stare at a gray spot, it will become white, while all the other spots remain gray. This is an example of 'irradiation' or 'brightness contrast'.