It is known from previous studies of the human brain that there exists an ordered mapping between the visual field and the primary visual cortex. However, 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. This mapping can be described by the term `cortical magnification factor' which refers to how many millimetres of cortex represent one degree of visual angle at any given eccentricity.
Non-invasive methods must be used to investigate the human brain. Visual stimuli elicit visual evoked scalp potentials (VEPs) generated by current sources located in the brain. The location of these sources can be estimated when the head is modelled as three concentric spherical shells and the neural sources are represented as dipoles. A series of experiments have been carried out using a red-green chromatic grating stimulus. This stimulus was presented in various positions in the visual field and VEPs were recorded. Estimating the neural source due to each stimulus and comparing its position with the position of the stimulus in the visual field will allow cortical magnification to be investigated. A novel mathematical formulation of cortical magnification will be presented, as will preliminary results from these experiments.