The efficiency of encoding: limits of information transfer into memory

We investigated how visual information is best presented to maximize the number of remembered items in a fixed time unit. In a memory task for images depicting real-world objects, we varied the number of images shown simultaneously, the presentation time, and the interstimulus interval (ISI). The viewing phase was followed by a two-alternative forced choice recognition task. We converted the percentage of correct answers into a capacity estimate scaled to a fixed time unit of 1 s to allow for comparisons across conditions. Our results showed that (1) presenting one image very briefly was always more efficient than simultaneously showing multiple images for longer periods; (2) for single images, the maximum encoding rate was fairly constant over a wide range of conditions, at 1.4 objects per second; (3) when testing was done a week later, memory capacity was the same for all conditions, irrespective of the presentation time and ISI at the initial viewing; (4) highly similar distractors led to worse performance than random distractors; and (5) showing an image twice for 100 ms was associated with worse performance than showing the image once, but for 200 ms.