The early stage of visual processing involves an array of spatio-temporal filters. We sought to investigate the number of temporal filters and their distribution across the retina. We did this by measuring temporal discrimination at threshold using a 2 x 2 forced-choice procedure. The stimuli were flickering 0.25 c/deg sinewave gratings, Gaussian weighted in both space and time. For each stimulus, the subject determined the interval which contained the stimulus (detection) and the temporal frequency at which the stimulus was presented (discrimination). Within the central 20 deg of the visual field, subjects were able to discriminate low from moderate or high temporal frequencies, suggesting that only two temporal filters exist centrally. Outside the central 20 deg of the visual field, subjects were able to discriminate both low from moderate and moderate from high temporal frequencies. The latter finding suggests that three temporal filters exist in the periphery. Thus, the numbers of filters within the central visual field and outside the central visual field are different.