Involvement of short-term memory in complex mental calculation.

The aim of this study was to examine the involvement of the short-term memory system in complex mental addition by manipulating the phonological and visual similarity of two numbers to be added. The phonological similarity of the problems appeared to have a major effect on both speed and accuracy. However, the manipulation of visual similarity failed to have any measurable impact. This suggests that the phonological loop, rather than the visual-spatial sketch pad, would be used preferably for temporary storage of addends. An interpretation of these results in terms of the nature of the internal code underlying this task is discussed.