An object at some distance from an observer will reflect light from the sun (or from an artificial source) in all directions, some of which will fall upon the corneae of the eyes where it will be focussed upon each retina, forming an image. The disparity between the electrical output of these two slightly different images is resolved either at the level of the lateral geniculate nucleus or in a part of the visual cortex called 'V1'. The resolved data is further processed in the visual cortex where some areas have specialised functions, for instance area V5 is involved in the modelling of motion and V4 in adding colour.