In message <3.0.16.19970210180913.3f576cd6@pop-3.ukonline.co.uk>, Tim Kerby writes >Its not the brain that is slow. It is retinal persistence that causes >images to merge. I recently made a light listner converting light to >sound. The ear can hear 50Hz mains hum for example and much above. I have >a 50Hz monitor and it flickers if I do not directly view it. Does the >retina respond slower in the center? The peripheral visual system is *much* more sensitive to movement (including flicker) than at the centre. This is very noticeable with flickering fluorescent lamps. Presumably we have evolved this way to detect predators creeping up on us from behind. Leon -- Leon Heller, G1HSM leon@lfheller.demon.co.uk Tel: +44 (0) 118 947 1424 (home) +44 (0) 1344 385556 (work)