Memory span for Arabic numerals and digit words: Evidence for a limited-capacity, visuo-spatial storage system

Six experiments examined the determinants of the numeral advantage effect: the finding that memory span for Arabic numerals (1, 2, 3, etc.) is greater than for digit words tone, two, three, etc.). The speed of item identifica tion for numeral and digit words was unrelated to memory span for the same items and a larger memory span for numerals persisted under concurrent rand om generation (Experiment 1). The numeral advantage, however, was abolished when the items were presented in random locations within an invisible 3 x 3 grid (Experiment 2) and in locations on a horizontal plane that ran contr ary to the natural direction of reading (Experiment 3). When the items were presented in the same location, a disruption of the spatial component of v isuo-spatial working memory eliminated the numeral advantage (Experiment 4) , whereas interference with the visual component of the system did not (Exp eriment 5). When the items were spatially distributed in a 3 x 3 matrix, ho wever, neither visual nor spatial interference abolished the effect (Experi ment 6). Taken together, these findings suggest that the numeral advantage effect is mediated by discrete components in visuo-spatial working memory d edicated to the temporary storage and renewal of visual codes and questions the assumption that the underlying mechanisms in immediate, visual serial recall are equivalent between stimulus categories.