 Wilkins et al 1980 found that paroxysmal activity in photosensitive epileptic patients can be triggered by binocular viewing of a large repetitive striped pattern with a spatial frequency of 1-4 cycles deg-1, a contrast of 10 or more, and a duty cycle of 50. Sensitivity to this visual pattern varies in the non-epileptic population Wilkins et al, 1984 but can produce unpleasant somatic e.g., eye-strain, headache and perceptual effects e.g., flicker, color illusions. This condition has been termed visual discomfort Wilkins et al., 1984 or visual stress Wilkins, 1995. 