A large number of studies have shown that the visual field can be mapped retinotopically in the primary visual cortex. The map of the retina on the cortex is referred to as a topographical map since adjacent points in the visual field map onto adjacent points in the visual cortex. Beyond this general agreement, there is disagreement as to the amount of cortex that is allocated to the representation of central vision or other portions of the visual field. The term 'cortical magnification factor' is used to refer to how many millimetres of cortex represent 1º of visual angle at any given eccentricity and thus it describes the scale of the retinotopic mapping.
One method of non-invasively investigating cortical magnification in humans is to use dipole source localization. A model of the primary visual cortex has been developed which represents both the upper visual cortex and lower visual cortex from one hemisphere of the brain as cylinders. Combining dipole source localization results from a pattern reversal VEP experiment with this cylinder model will enable an estimate of human cortical magnification to be developed. Preliminary results from these models will be presented and their extension to a three-dimensional realistic model of the primary visual cortex will be discussed.