Two basic illusion which helps in interface design.
While designing interface you should focus the understanding of human psychology. How we interpret the visual signals? The way things are and the way we perceive them. Taking care of distances, color schemes and the contextual objects. For example, if you want a user to error message at the bottom of the screen, It had better be flashing. Our expectations affect the way an image is perceived. Our perception of size is not completely reliable. So the following are illusions which are based on size of objects and help in understanding interface design.
The Ponzo Illusion:
An optical illusion in which two identical figures are made to appear of different sizes because of the effect of perspective. The optical illusions in which two identical lines appear to be different sizes, because they’re overlying a separate diminishing set of parallel lines.
The Ponzo Illusion plays upon how we perceive size. The mind, Ponzo postulated, relies on background context to judge the sizes of things that it’s looking at. Remove or distort that context, and ultimately your brain can be tricked into making misjudgments. In the Ponzo Illusion, it’s the forced perspective created by the underlying lines that causes all the problems.
By overlaying two identical lines over a diminishing series of converging lines, like train tracks, the Ponzo Illusion tricks our brain into presuming that the upper of the two lines must be longer, because it appears — due solely to its background — to somehow be “in the distance.” So to be of anywhere near the same size to the lower lines, the top line must be larger because we perceive it as being “further away.” It isn’t, of course, because we’re looking at a flat picture. But because of our perception of the forced perspective in the background, we get confused and make a misjudgment.
The Muller-Lyer illusion:
The Muller-Lyer illusion is a well-known optical illusion in which two lines of the same length appear to be of different lengths.
In the image above, which line appears the longest? For most people, the line with the fins of the arrow outward appears to be the longest while the line with the arrow fins pointing inwards appears shorter. While your eyes might tell you that line in the middle is the longest, the shafts of both lines are exactly the same length.
