Primary Visual Cortex Essay

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What is wrong with the idea that human visual perception is achieved by a single area of the brain that simply reflects the visual information coming from the eyes?

In the eighteenth and nineteenth centuries philosophers believed that our brains perceived or made sense of the visual information received through our eyes by seeing it as a direct representation of what we are looking at. However, some of today’s researches in cognitive science have assumed a different method.

Helmholtz and Fechner were the two major front runners who were involved in the development of ideas on visual perception. Fechner has an impact on later studies because he saw the difference between inner and outer psychophysics. His theories created a springboard for other practitioners in the field to investigate the processes by which information is processed in the brain. Helmholtz argued that ‘the process of perception takes place in the brain, following transmission of neural signals from sensory receptors and the brain only has indirect access to the external world via sense’(Wade et al,2001,67p). Later, Wurz and Kandel argued about binding mechanism and they believed that ‘There must be a mechanism by which the brain momentarily associates the information being processed independently by different all populations in different cortical regions. For if perceiving involves an internal picture or image of the external scene, the picture must be constructed and the image built up’ (Bennett et al, 2003, 140p). Modern theory has been argued by Wilhelm Wundt. He thought that higher mentally systems cannot be studied via experiments. He believed that these have to be treated as a cultural science. Nowadays, with the development of medical science it has been possible to show that visual perception is a much more complex process and it is also the most complex among all of sensory system.

The eye can divide for two systems. One system responsible for shaping the image and the other one is specialised for transforming the electric impulses. To perceive objects we have sensory detectors in the retina that respond to reflected light and these are known as Rods and Cones.( Atkinson et al, 2005) Rods are mostly found in the outer area and they respond to different intensities of light and are responsible for vision in dim light and for detecting movement. Cones are mostly found in Fovea or central part of the retina. They operate at a higher level of stimulation and differ in their sensitivity to different wavelengths of light and they are essential for colour and sharpness of vision. The ganglion cells of the retina provide the visual pathway to the lateral geniculate nucleus (LGN) of the thalamus which transmits information to the primary visual cortex. This visual pathway known as the retina-geniculate-striate pathway which is the main pathway between the eye and the cortex is divided into two separate pathways, the Parvocellular (P) and Magnocellular (M) pathways. While the P pathway carries information about form and colour, the M pathway about movement. From the nasal part of the retina information crosses over to the contra lateral side of the brain and from the temporal part information stays on the ipsilateral side so that each visual field appears on the contra lateral primary visual cortex (V1). (Eysenck et al., 2005)

It has been argued that visual processing takes place within two partially independent visual sub-systems called ventral- and dorsal pathways. This theory assumes that conscious visual perception is separate functions of the visual system, medicated by different neural pathways. The Ventral pathway is responsible for form and colour perception and also object recognition whereas dorsal pathways are specialised for extracting information on the size and location of the object. It has been shown how visual information is transferred from the retina to the LGN and how
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