The conversation between human and AI assistant.
[|Human|] Jot down some important points about optical illusion from the given passage.
[|AI|] 1. Visual Illusion is caused by theÂ visual systemÂ and characterized by a visualÂ perceptÂ that appears
to be different fromÂ reality.
2. According to Richard Gregory a classification proposed byÂ him is useful as an orientation that,
there are three main classes: physical, physiological, and cognitive illusions, and in each class
there are four kinds: Ambiguities, distortions, paradoxes, and fictions.
3. An example for a physical distortion would be the apparent bending of a stick half immerged in
water; an example for a physiological paradox is theÂ motion aftereffectÂ (where, despite
movement, position remains unchanged).Â 
4. An example for a physiological fiction is anÂ afterimage
5. Three cognitive distortions are theÂ  Ponzo ,Â Poggendorff, andÂ MÃ¼ller-LyerÂ illusion.
6. Physical illusions are caused by the physical environment, e.g. by the optical properties of
water. Physiological illusions arise in the eye or the visual pathway.
7. The most widely know illusion is visual illusions which are the result ofÂ unconscious inferences.
[|Human|] 
Jot down some important points about optical illusion from the given passage.