View source for Visual perception

===Early studies===<!--[[Intromission theory]] and [[Intromissionism]] redirect here-->
[[File:Ventral-dorsal streams.svg|thumb|upright=1.3|The visual [[dorsal stream]] (green) and [[ventral stream]] (purple) are shown. Much of the human [[cerebral cortex]] is involved in vision.]]

There were two major [[ancient Greek]] schools, providing a primitive explanation of how vision works.

The first was the "[[Emission theory (vision)|emission theory]]" of vision which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If an object was seen directly it was by 'means of rays' coming out of the eyes and again falling on the object. A refracted image was, however, seen by 'means of rays' as well, which came out of the eyes, traversed through the air, and after refraction, fell on the visible object which was sighted as the result of the movement of the rays from the eye. This theory was championed by scholars who were followers of  [[Euclid]]'s ''[[Euclid's Optics|Optics]]'' and [[Ptolemy]]'s ''[[Optics (Ptolemy)|Optics]]''.

The second school advocated the so-called 'intromission' approach which sees vision as coming from something entering the eyes representative of the object. With its main propagator [[Aristotle]] (''[[Sense and Sensibilia (Aristotle)|De Sensu]]''),<ref name=Finger>{{cite book |last=Finger|first=Stanley |title=Origins of neuroscience: a history of explorations into brain function |publisher=Oxford University Press |location=Oxford [Oxfordshire] |year=1994 |pages=67–69 |isbn=978-0-19-506503-9 |oclc=27151391 }}</ref> and his followers,<ref name=Finger/> this theory seems to have some contact with modern theories of what vision really is, but it remained only a speculation lacking any experimental foundation. (In eighteenth-century England, [[Isaac Newton]], [[John Locke]], and others, carried the '''intromission theory'''<!--boldface per WP:R#PLA--> of vision forward by insisting that vision involved a process in which rays—composed of actual corporeal matter—emanated from seen objects and entered the seer's mind/sensorium through the eye's aperture.)<ref>{{cite journal | author = Swenson Rivka | year = 2010 | title = Optics, Gender, and the Eighteenth-Century Gaze: Looking at Eliza Haywood's Anti-Pamela | journal = The Eighteenth Century: Theory and Interpretation | volume = 51 | issue = 1–2| pages = 27–43 | doi = 10.1353/ecy.2010.0006 | s2cid = 145149737 }}</ref>

Both schools of thought relied upon the principle that "like is only known by like", and thus upon the notion that the eye was composed of some "internal fire" that interacted with the "external fire" of visible light and made vision possible. [[Plato]] makes this assertion in his dialogue ''[[Timaeus (dialogue)|Timaeus]]'' (45b and 46b), as does [[Empedocles]] (as reported by Aristotle in his ''De Sensu'', [[Diels–Kranz numbering system|DK]] frag. B17).<ref name=Finger/>

[[File:Eye Line of sight.jpg|thumb|[[Leonardo da Vinci]]: The eye has a central line and everything that reaches the eye through this central line can be seen distinctly.]]

[[Alhazen]] (965 – {{circa}} 1040) carried out many investigations and [[experiment]]s on visual perception, extended the work of Ptolemy on [[binocular vision]], and commented on the anatomical works of Galen.<ref name=Howard>{{cite journal |last=Howard|first=I |title=Alhazen's neglected discoveries of visual phenomena |journal=Perception |volume=25 |pages=1203–1217 |year=1996 |doi=10.1068/p251203 |pmid=9027923 |issue=10|s2cid=20880413 }}</ref><ref name=Khaleefa>{{cite journal |first=Omar |last=Khaleefa |year=1999 |title=Who Is the Founder of Psychophysics and Experimental Psychology? |journal=American Journal of Islamic Social Sciences |volume=16 |issue=2 |pages=1–26|doi=10.35632/ajis.v16i2.2126 }}</ref> He was the first person to explain that vision occurs when light bounces on an object and then is directed to one's eyes.<ref>{{cite book|last=Adamson|first=Peter|title=Philosophy in the Islamic World: A History of Philosophy Without Any Gaps|url=https://books.google.com/books?id=KEpRDAAAQBAJ|date=7 July 2016|publisher=Oxford University Press|isbn=978-0-19-957749-1|page=77}}</ref>

[[Leonardo da Vinci]] (1452–1519) is believed to be the first to recognize the special optical qualities of the eye. He wrote "The function of the human eye ... was described by a large number of authors in a certain way. But I found it to be completely different." His main experimental finding was that there is only a distinct and clear vision at the line of sight—the optical line that ends at the [[Fovea centralis|fovea]]. Although he did not use these words literally he actually is the father of the modern distinction between foveal and [[peripheral vision]].<ref>{{Cite journal|last=Keele|first=Kd|date=1955|title=Leonardo da Vinci on vision.|journal=Proceedings of the Royal Society of Medicine|volume=48|issue=5|pages=384–390|issn=0035-9157|pmid=14395232|pmc=1918888|doi=10.1177/003591575504800512}}</ref>

[[Isaac Newton]] (1642–1726/27) was the first to discover through experimentation, by isolating individual colors of the spectrum of light passing through a [[Prism (optics)|prism]], that the visually perceived color of objects appeared due to the character of light the objects reflected, and that these divided colors could not be changed into any other color, which was contrary to scientific expectation of the day.<ref name="Margaret. 2008" />