The visual system is the whole of the Organe S taking part in the visual perception, of the Rétine to the sensorimotor system. Its role is to perceive and interpret two images in two dimensions in an image in three dimensions. It is mainly made up of:

The eye and the optical nerve

See also: Vision

The light enters the eye where it is collected by the Rétine. There is transduction electromagnetic information in potential of actions. The image is then analyzed with the center even of the retina in zones of Contraste and the output this is sent to the remainder of the visual system by the Optical nerve. At the human ones, the visual system is only the sensory Système with being directly connected, via the Optical nerve, with the Cerveau, had with the need for processing the visual information quickly. nap to Be miraculous. The eye functions remarkably like has CCC camera, taking Visible light and converting it into has stream off information that edge Be transmitted via Nerve S.

Light enters the eye, passing through the Cornea and the Pupil (controlled by the iris) and is Refracted by the lens. The lens inverts the light and projects year image onto the Retina.

The retina consists off has broad number off " receptor" concealments and contain has particular protein molecule called Rhodopsin. When rhodopsin is struck by has Photon (particle off light has) it transmits has signal to the concealment; the more photons strike the concealment, the stronger the signal will Be. In nap animals, like humans, Cone concealment S contain cone opsin molecules attuned to specific Wavelength S off light; i.e., has blue cone concealment contains opsin most attuned to blue-wavelength light and will most strongly Be stimulated by blue-wavelength light, while has yellow-red cone concealment will only Be weakly stimulated by blue-wavelength light. This gives the ability to distinguish Color .-->

Chiasma and optical tract

See also: optical Chiasma

The optical nerves of each eye meet on the level of the optical Chiasma, which makes it possible to redistribute the visual information according to whether it is in the right part or the left part of the Field of vision (each eye sees on the left and on the right at the same time). The left hémichamp goes in the hemisphere right and vice versa (there is an inversion).

The continuation of the optical nerves after the chiasma is called the optical Tractus. In each hemisphere, it distributes the visual information to different of which the side geniculate Corps. The latter is particular because it is him which sends the information which will be analyzed by the visual Cortex to give conscious visual perception in particular.

Side geniculate body

The side geniculate Corps is a core relay, located at the level of the Thalamus, which allows the transfer of the information of the eyes towards the visual Cortex. One believed during a certain time that it was the simple one and single relay of visual perception. In fact, it is not only receiving visual information (see higher) and the information which it receives does not come only from the eyes.

Alternate ways of the vision

The relay of visual fibers on the level of the side geniculate Corps allows approximately 10% those to project directly in the higher Colliculus. Experiments (Weiskrantz, 1973) carried out on subjects having undergone a surgical ablation of the visual Cortex primary showed that those have a subconscious visual capacity however, and that they remain able to locate objects, to determine the orientation of it, if required to perceive the color of it, but not to compare them with consciously perceived objects (in the event of unilateral ablation). The feeling is thus not exploitable by the subject (intuitive) and does not appear, except for objects moving, in a spontaneous way. This phenomenon is named blindslight in English.

Complementary experiments (Nakamura and Mishkin, 1980-1986) showed that one could cause blindness conscious by completely isolating the visual Cortex primary education from the remainder of brain, even if the optical tract remained intact. The visual conscience would thus result from a complex process of dialog between cortical perception “traditional” of the V1 zone, the other cortical zones V and the subcortical or thalamic ways “unconscious” (Weiskrantz, 1999).

Two zones of the cortex préfontal (Brodmann 9 and 46 right-hand side) were identified in the mechanism of conscious vision. 9 could correspond to a zone of discrimination between conscious and subconscious vision, and 46 would integrate and synthesize cortical and thalamic visual perceptions (Barbur, Sahraie, Weiskrantz, 1996).

Optical radiations

The nervous fibers which connect the side geniculate body to the visual cortex constitute the optical Radiation of a hemisphere. A lesion of an optical radiation led to the loss partial or total of the vision in the hemisphere concerned (a anopsy). It is thus by this way that is made visual perception Consciente.

Visual cortex

See also: visual Cortex

The visual Cortex is the most imposing system in the human brain and is responsible for the image processings. It carries out Traitement S of low level (orientation, contours) but so high level (forms, movements).

Simple: Visual system Zh-min-nan: Sī-kak hē-thóng

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