Visual data is created by the eye sensing its environment.
Perception is simply a person's use of one or more senses. A human observes outside phenomenon through sight, smell, touch, taste and hearing. Visual perceptions are transferred from the corresponding sensing part of the brain, the visual cortex, to the cognitive part, known as the cerebral cortex. What a person thinks about a visual observation is dependent on the sensory data itself. Naturally, if the sensory data is inaccurate, the person's cognition regarding that observation will be incorrect. The Gestalt School of Psychology determined six properties of visual data: proximity, continuity, closure, enclosure, similarity and connection. Erroneously perceiving these properties contribute to the ease in which visual perception can be tested. These experiments are called optical illusions.
The Broken Stick
Water distorts visual perception, creating images that are hardly what they seem.
Optical illusions often occur in nature, causing even the most ancient of human philosophers to question the reliability of human visual perception. Rene Descartes' presentation of Cartesian Skepticism is one of the most popular philosophical pieces addressing visual perception's unreliability. He introduces the "stick in water" experiment, where a stick is submerged halfway in and halfway out of a glass of water. Based on visual perception alone, the stick appears broken.
The Stroop Effect
Visual perception experiments often involve color tricks.
The Stroop Effect is another visual perception experiment. The Stroop Effect occurs when the names of several colors are written on a black background, with each color name written in a color different than that which it spells. For example, the word "red" is written with a blue marker. When a person reads the colors aloud, he or she often says the color of the text as opposed to the written word itself.
Two-dimensional Images
Salvador Dali created two-dimensional art that confuses visual perception.
Many artists create two-dimensional illustrations that test the reliability of human perception. A very common illustration is a black-and-white drawing called the "Face Vase," where the white graphic looks like a vase and the surrounding black graphics look like two faces. Looking at the illustration, the observer cannot tell which item is in the foreground and which is in the background, and both images are seemingly present at the same time. M. C. Escher, Salvador Dali and Roger Shepard are popular artists specializing in visual perception illusions.
Afterimages
Staring at a black-and-white image and then glancing at a white wall causes an afterimage.
More experiments target what is called the afterimages, or the illusion appearing when the eye still "sees" an object, despite no longer looking at it. This is easily tested by fixating on an object, usually a black-and-white pattern, for about thirty seconds, and then moving your line of vision away from the object and onto a white surface. The image still appears, but the colors are negated. This is also tested by staring at a light for a short period of time, and then turning the light off. The shadowy image of the light is still visible, even though it is not real. This happens because nerve receptors in the eye become fatigued.
Tags: visual perception, Stroop Effect, reliability human, Salvador Dali, sensory data, visual perception