Digit memory of grand experts in abacus-derived mental calculation

Abstract

Three abacus-derived mental arithmetic experts were given various memory tasks. They had a much larger digit span than the average, but their span for letters of the alphabet or fruit names was not unusual. They could reproduce digits, but not object names, backwards as quickly as forwards; their memory for digits, but not for letters, was to some extent compatible with a preloaded memory for fruit names; their digit memory was disrupted more by concurrent visual-spatial tasks than by aural-verbal tasks while the reverse was true for their memory for letters. In these characteristics their digit memory differed significantly from that of the control subjects who had had negligible experience in abacus operation, while there was no difference in the memory for non-digit materials. After other series had been memorized, the experts could not recall any part of the preceding series, nor could they recognize it, though they could retain completely a near-span digit series for 30 seconds. They seemed to have a ‘mental abacus’ or specific device to represent visuo-spatially a number comprising many digits just long enough for calculation.