The ability of Visual Perception
In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. The resulting perception is also known as eyesight, sight or vision. The various components involved in vision are known as the visual system.
The visual dorsal stream (green) and ventral stream (purple) are shown. Much of the human cerebral cortex is involved in vision. The visual system allows us to assimilate information from the environment to help guide our actions. The act of seeing starts when the lens of the eye focus an image of the outside world onto a light-sensitive membrane in the back of the eye, called the retina.
The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals. The lens of the eye focuses light on the photoreceptive cells of the retina, which detect the photons of light and respond by producing neural impulses. These signals are processed in a hierarchical fashion by different parts of the brain, from the retina to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain.
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 we actually see.
There were Two major Grecian schools, providing a primitive explanation of how vision is carried out. The first was the “emission theory” which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. . If we saw an object 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. Although this theory was championed by scholars like Euclid and Ptolemy and their followers, and was believed by Descartes.
The second school advocated the so called the `intromission’ approach which sees vision as coming from something entering the eyes representative of the object. With its main propagators Aristotle, Galen and their followers, this theory seems to have touched a little sense on what really vision is, but remained only a speculation lacking any experimental foundation.