Memory for the order of briefly presented numerals in humans as a function of practice

Inoue and Matsuzawa (Curr Biol 17: R1004-R1005, 2007) showed that with an accuracy of approximately 79%, the juvenile chimpanzee, Ayumu, could recall the position and order of a random subset of five Arabic numerals between one and nine when those numerals were presented for only 210 ms on a computer touch screen before being masked with white squares. None of nine humans working on the same task approached this level of accuracy. Inoue and Matsuzawa (2007) claimed this performance difference was evidence of a memorial capacity in young chimpanzees that was superior to that seen in adult humans. While the between-species performance difference they report is apparent in their data, so too is a large difference in practice on their task: Ayumu had many sessions of practice on their task before terminal performances were measured; their human subjects had none. The present report shows that when two humans are given practice in the Inoue and Matsuzawa (2007) memory task, their accuracy levels match those of Ayumu.