Editing Illusion (section)

==Visual==
{{main|Optical illusion}}
[[File:Living_gecko_hunting_the_pointer_of_a_mouse.webm|thumb|Example of visual illusion: a real [[gecko]] hunts the [[Mouse pointer|pointer of a mouse]], confused with a [[predation|prey]]]]
[[File:Checker shadow illusion.svg|thumb|right|An optical illusion. Square A is exactly the same shade of grey as Square B. (See [[Checker shadow illusion]].)]]

A [[visual illusion]] or optical illusion is characterized by [[Visual perception|visually perceived]] images that are deceptive or misleading. Therefore, the information gathered by the visual sense is processed to create a [[percept]] that does not tally with information from other senses or physical measurements.<ref name=":02">{{cite journal |last1=Gross |first1=L. |date=2006 |title=Classic Illusion Sheds New Light on the Neural Site of Tactile Perception. |journal=PLOS Biol |volume=4 |issue=3 |pages=e96 |doi=10.1371/journal.pbio.0040096 |pmc=1382017 |pmid=20076548 |doi-access=free }}</ref>

The visual system, which includes the eyes (namely the retinas) and the central nervous system (namely the brain's visual cortex), constructs reality through both perceptual and cognitive neural pathways. Visual illusions are (at least in part) thought to be caused by excessive competing stimuli. Each stimulus follows a dedicated neural path in the early stages of visual processing, and intense/repetitive activity or interaction with active adjoining channels (perceptual neural circuits, usually at the same level) causes a [[physiological]] imbalance that alters perception. During low-level visual processing, the retinal circuit arranges the information in the photoreceptors, by creating initial visual percepts from the patterns of light which fall on the retina. The Hermann [[grid illusion]] and [[Mach bands]] are two illusions that are widely considered to be caused by a biological phenomenon named [[lateral inhibition]], where the receptor signal in the retina's [[Receptive field|receptive fields]] from light and dark areas compete with one another.<ref name=":12">Kandel E.R., & Schwartz J.H., & Jessell T.M., & Siegelbaum S.A., & Hudspeth A.J., & Mack S(Eds.), (2014). ''Principles of Neural Science, Fifth Edition''. McGraw Hill.</ref>

The assembly of visual elements into a collective percept, that distinguishes objects from backgrounds, takes part during intermediate-level visual processing. Many common visual illusions are a consequence of the percept constructed during this processing stage, as the elements first captured during low-level processing might easily be interpreted to form an image that differs from objective reality. An example is when two objects of the same size are placed on a certain background which conditions us to believe that one object might be larger than the other, and when the background is removed or replaced our perception immediately changes to the correct scenario (effectively concluding that both objects have equal dimensions).<ref name=":12" />

High-level visual processing consolidates information gathered from various sources to apply cognitive influences that create a conscious visual experience. Thus, allowing us to recognize the complex identity of different elements, and the disparate relations between them through cognitive processes. Visual illusions are also often a product of this processing stage, and it is during this stage that we might ultimately become conscious of any optical illusion. There are two crucial properties of our visual system related mostly to high-level visual processing, referred to as selectivity and invariance (which we have consistently attempted to replicate in image recognition computer algorithms). Selectivity refers to the identification of particular features that are relevant to recognize a specific element or object, while abstracting from other features that are not fundamental to performing the same recognition (e.g. when we see the shape of a house, certain contours that are essential for us to recognize it while other contours or image properties are not, such as color). On the other hand, invariance refers to the ability to be indifferent to small variations of a given feature, effectively identifying all those variations as simply being different versions of the same feature (e.g. we can recognize a given handwritten letter of the alphabet, written by different people with distinct styles of calligraphy).<ref name=":12" />

The whole process that constructs our visual experience is extremely complex (with multiple qualities that are unmatched by any computer or digital system). It is organized by many sequential and parallel sub-processes, each of which is essential in building our conscious image of the world. Our whole visual system seeks to simplify and categorize the unstructured low-level visual information, through both selectivity and invariance. Thus, while trying to organize an image by "filling in the gaps" through assumptions, we become vulnerable to misinterpretation.<ref name=":22">[http://www.technologyreview.com/read_article.aspx?id=17363&ch=biotech&sc=&pg=1 The Cutting Edge of Haptics] (MIT [[Technology Review]] article)</ref><ref name=":32">{{Cite web |title=Robles-De-La-Torre & Hayward 2001 |url=http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf |url-status=dead |archive-url=https://web.archive.org/web/20061003225801/http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf |archive-date=2006-10-03 |access-date=2006-10-03}}</ref>