Thirty subjects participated in a letter-matching reaction time task requiring physical identity and vowel/consonant judgments. Stimulus onset asynchronies (SOAs) of 100, 200, and 500 msec were used. For the continuous group, the first letter remained on through the trial; for the discrete group, the first letter was presented for 50 msec; for the white field group, the first letter was presented ... [Show full abstract] for 50 msec followed immediately by a 40-msec white field. In all groups, physical matches were faster than vowel/consonant matches. Reaction times for the continuous and discrete groups decreased to a minimum at 500 msec SOA. For the white field group, fastest reaction times occurred at 100 msec and increased to a maximum at 500 msec SOA. The difference in functions was attributed to differential memory demands in the groups.