Simultaneous better than sequential for brief presentations

During perceptually intensive tasks such as reading, there is a bottleneck in the information transfer between the large number of alphanumeric characters available and the acquiring of these characters. This is due mainly to the limited number of characters that one can report at a glance (also known as the "magic number 7 +/- 2") [Psychol. Rev. 63, 81 (1956)]. To examine where in the perceptual pathway this bottleneck occurred, several investigators tested and compared performance with simultaneous and with sequential target presentations [J. Exp. Psychol. 79, 1 (1969); 93, 72 (1972); Percept. Psychophys. 14, 231 (1973)]. They found that performance was nearly equal in the two cases and concluded that the bottleneck must be due to the limitation of short-term memory. However, these studies were limited either by a long stimulus-onset asynchrony (SOA), or time interval between onsets of icon presentations, or by a lack of poststimulus masking. We report on experiments designed to overcome these limitations. We used shorter SOA's than did previous investigators, and we removed persistence effects by poststimulus masking. Our stimuli were presented either sequentially or simultaneously. For the sequential presentation a numeral ranging from 0 to 9 was displayed at any one of eight positions 1.5 deg from a central fixation cross. The appearance of the next numeral in another part of the display coincided with the masking of the previous numeral. This was done for trials of one to four numerals and SOA's of 16.7, 33.3, and 50.0 ms.