Types of Optical Illusions

Literal illusions are the type of illusion that are seen in daily life. Seeing a hand at the window when instead it is just a tree branch or seeing a person in your room when it is just a stack of clothes, these are literal illusions. The name meaning the optical illusions are literal illusions made through our physical environments.

Physiological illusions are the illusions that use color and motion to create an after-effect image, first mentioned by Aristotle. An example of this is the Waterfall Illusion. To experience this illusion, stare at a waterfall for a few minutes; after shifting your gaze, stationary objects such as the nearby rocks will briefly appear to crawl upward (Eagleman 2002). Another example of this is Hermann's Grid, a black and white grid that seems to appear gray dots in intersections when there isn't any.

Cognitive illusions were presented by Hermann von Helmholtz. Helmholtz explained that our mind makes assumptions about the environment around us and therefore leads to unexplainable events (Gourley 2019). Within cognitive illusion there are four subgroups: ambiguous illusions, paradox illusions, distorting illusions, and fiction illusions.

Ambiguous illusions are images that shift on the perception of the viewer. These illusions are called impossible images (Sincero 2013). Impossible in the way that you can't have two things exist in one picture. Two popular examples of these illusions are the young lady and the old lady and the Necker's cube. In the young lady and old lady illusion you may see at first glance a young lady with a necklace turned away from you, but as you focus on the image your perception can change to an old lady with a large nose turned towards you but slightly looking away. The Necker's cube changes on what you as the viewer decide to see the cube as, meaning that either the cube is seen with the lower square being the front of the cube or the higher square being the front of the cube. Paradox illusions are illusions that are paradoxical in its existence. These are impossible objects. Impossible in the way that physics and the 3-dimensional space can't explain how the objects are possible. Have you seen the staircase that never ends, also known as the Penrose stairs, or the Penrose triangle? The never-ending staircase seems to be going up every step and yet you end up in the same place you started. The Penrose triangle, a3D triangle in which if you were to roll a marble across the surface it would touch all surfaces of the triangle, in a continuous loop. Distorting illusions, also known as geo-metical optical illusions, distort size, length, curvature, and position to create an image that seems contorted (Sincero 2013). Examples of these are the cafe wall and the Ponzo illusion. The cafe wall illusion gives parallel lines that are offset with checkerboard tiles in between. Because the tiles are offset, it seems as if the lines are slanted and not parallel at all. The Ponzo illusions sets up two lines on a railroad perspective. The line farther in the distance seems longer than the line that is closer, but in fact these lines are the same length. In fiction illusions, the viewer creates an object that doesn't actually exist in the image. In other words, put by Piper Gourley is, a fiction illusion is an illusion which exists entirely as a product of the mind that is only visible to one individual. Examples of these types of illusions are the Kanizsa triangle and the Subjective Necker's Cube. These two images show a triangle and a cube that are not really there.