2 microgenetic hypotheses were tested: perception would become more stable with an increase in duration of viewing; and this increase is different for form and for size. 100 plane figures, all combinations of 10 heights and 10 widths varying in increments of .01 in., constituted the stimulus set. They were presented singly as back-lighted figures in a completely dark surround. 7 male Ss had at least 20-20 vision uncorrected or with contact lens. There were 9 durations of viewing and 2 types of judgments: form, squares and rectangles, or size, large and small. Discrimination measures were computed and showed that Ss could discriminate form better than they could discriminate size. There was no significant effect of duration on either type of discrimination, nor was there any interaction between type of judgment and duration.