 A. Noisy visual system. Working from a model of visual epilepsy, Wilkins 1986 has proposed that visual discomfort is caused by hypersensitivity in some cortical cells that share sensitivity for a particular spatial frequency and orientation. Several studies have examined the contrast sensitivity functions CSF of high visual discomfort individuals and found weaker sensitivity at intermediate Wilkins et al., 1984 and sometimes at higher spatial frequencies Conlon, Lovegrove, Barker, Chekaluk, 2001. A recent pilot study of ten children with visual discomfort found differences in visual evoked potential VEP amplitudes among those with a history of headache and migraines Riddell, Wilkins, Hainline, 2006. 