Biomedical Engineering Reference
In-Depth Information
Fig. 2
Visual pathway ( a ) with the detailed visual cortex topography ( b )
as radix optica mesencephalica and other fibres end in the lateral geniculate nucleus.
Here the axons of the ganglion cells connect to the last neuron of the visual pathway
(Fig. 2 a). The axons of the fourth neuron constitute the tractus geniculocorticalis and
terminate in the occipital lobe cortex (visual cortex) where they form the cortical
image of the external world. The visual cortex is divided by its function into five
smaller areas called V1-V5 (Fig. 2 b). V1 area is the most studied part of the visual
cortex from the point of image processing. It is divided into six main layers. V1
cells are similar with circle symmetry to retinal ganglion cells or lateral geniculate
nucleus cells. They have receptive fields divided into inhibit and exhibit areas. These
areas are not radial symmetric but they have oriented receptive fields with reaction
to the specific space oriented stimulus (edge orientation, spatial frequencies, space
locations, time frequencies and their combinations) [ 2 ]. From the V1 area is the
image information send to the higher layers V2-V5 that are responsible for the
complicated task of the vision process. These areas are still in the centre of the
research. It is known e.g. that V4 is responsible for color vision and V5 for temporal
vision. More in [ 1 - 7 ].
1.1.2
Eye Movements
Eye movements are a result of contracting and relaxing six ocular muscles. In
physiological conditions multiple muscles are activated during eye movement,
thus, muscles have more functions depending on the initial eye position. The
movement of only one eye is called duction; the movement of both eyes with the
same direction is version (dextroversion, levoversion, supraversion, infraversion).
The opposite movement of the eyes is called vergence (convergence is medial
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