What is Illusion?
{{No sources|date=November 2024}}[[File:Café wall.svg|thumb|The café wall illusion: the horizontal lines are parallel, despite appearing to be at different angles to each other]] [[File:Brunnen Ahmedabad.jpg|thumb|Illusionː The ''Flying tap'' fountain in [[Ahmedabad]] seems to hang in the air. In reality, there is a tube in the middle of the water, which supports it.]] An '''illusion''' is a change of [[perception]]. The [[brain]] arranges, sorts, and organises [[data]] from the [[senses]]. Normally the system works well. Sometimes it does not, and we see illusions. In general, they are shared by most people in the same situation. Illusions can happen with all five [[Sensory system|senses]] ([[taste]], [[touch]], [[sight]], [[Olfactory system|smell]], and [[hearing]]), and some involve the way information from two senses is put together. Some illusions happen because of [[disorder]]s, but generally, all normal people can sense the same illusion. An illusion is different from a [[hallucination]]. A hallucination is sensing something [[Psychosis|that is not real]], but an illusion is interpreting what we sense wrongly. == Types of illusions == === Optical illusions === [[Optical illusion]]s are the best known and understood. Because they are illusions common to most people, it follows that they are a product of the [[visual system]]. The visual system, from the [[retina]] to the [[visual cortex]], is what is common to most humans. === Auditory illusions === These are illusions which are heard. The person listening hears sounds that aren’t really there, or sounds that can’t really happen. A [[Shepard]] tone is an auditory illusion. === Touch illusions === They are when a person feels something that is not there, or something that should not be there but feels like it is. This happens sometimes when a person [[Amputation|loses their arm]]. The person still feels like the arm is there. They might want to scratch the arm, or the arm might hurt them. This can happen with any limb of the body, and it is called