Judging the Order of Visual Stimuli

Abstract
Psychometric functions obtained for judgements of the order of two long duration light flashes were about half as steep as those previously obtained for short flashes. The range from 50 to 75 per cent correct judgements corresponded to interstimulus intervals from 36 to 98 msec. in the 6 subjects tested. Stimuli ½ degree above and below the fixation point produced slightly more accurate judgements than pairs of stimuli 2 degrees above and below this point. The shape of the curves did not conform to a normal ogive of the kind normally expected in threshold determinations. These data may be explicable in terms of a visual sampling mechanism capable of being triggered by incoming stimuli.