– Written by Alan Tathanhlong
Have you ever looked at pictures that tricked your eyes into seeing something else, rather than what was actually there? If so, that’s what we call optical illusions! An optical illusion is a visual of seeming to see something that does not exist or that is other than it appears. Optical illusions are quite different from illusions that come from the art of magic, which are able to fool the mind with their secrets and sleights of hand. Some optical illusions can make you imagine different pictures, even though the artist of these optical illusions depicted a much different image all together. Today, we will be talking about different types of optical illusions that are simple, yet can create a variety of images in the eye.
- Grid Illusion – The grid illusion is any kind of grid that deceives a person’s vision. The two most common types of grid illusions are the 1870 Hermann grid illusion and the 1994 scintillating grid illusion. The Herman grid illusion is characterized by “ghostlike” grey blobs perceived at the intersections of a white (or light-colored) grid on a black background. The grey blobs disappear when looking directly at an intersection. The scintillating grid illusion, however is constructed by superimposing white discs on the intersections of orthogonal gray bars on a black background. Dark dots seem to appear and disappear rapidly at random intersections, hence the name. When a person keeps his or her eyes directly on a single intersection, the dark dot does not appear. The dark dots disappear if one is too close to or too far from the image.
- Ponzo Illusion – In the 1911 Ponzo illusion, two identical lines across a pair of converging lines, similar to railway tracks, are drawn. The upper line looks longer because we interpret the converging sides according to linear perspective as parallel lines receding into the distance. In this context, we interpret the upper line as though it were farther away, so we see it as longer – a farther object would have to be longer than a nearer one for both to produce retinal images of the same size.
- Penrose Triangle and Penrose Stairs – Finally, these two optical illusions are slightly different, but they follow the same guidelines. The Penrose stairs was created by Lionel Penrose and his son Roger Penrose. A variation on the Penrose triangle, it is a two-dimensional depiction of a staircase in which the stairs make four 90-degree turns as they ascend or descend yet form a continuous loop, so that a person could climb them forever and never get any higher. However, the original Penrose triangle, created by the Swedish artist Oscar Reutersvärd in 1934, was independently devised and popularized by the mathematician Roger Penrose in the 1950s, describing it as “impossibility in its purest form”.