Study
See also: Two-streams hypothesis
The major problem in visual perception is that what people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Thus people interested in perception have long struggled to explain what visual processing does to create what is actually seen. # ISO certification in India
Early studies
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” 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 Optics and Ptolemy’s Optics.# ISO certification in India
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 (De Sensu), and his followers,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 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.) # ISO certification in India
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” which interacted with the “external fire” of visible light and made vision possible. Plato makes this assertion in his dialogue Timaeus (45b and 46b), as does Empedocles (as reported by Aristotle in his De Sensu, DK frag. B17).
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 – c. 1040) carried out many investigations and experiments on visual perception, extended the work of Ptolemy on binocular vision, and commented on the anatomical works of Galen. He was the first person to explain that vision occurs when light bounces on an object and then is directed to one’s eyes. # ISO certification in India
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. Although he did not use these words literally he actually is the father of the modern distinction between foveal and peripheral vision. # ISO certification in India
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, 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. # ISO certification in India