Arithmetic operation and working memory: differential suppression in dual tasks.

The relationship between arithmetic function and working memory was examined using a dual-task paradigm for either phonological or visuo-spatial suppression. Simultaneous phonological rehearsal significantly delayed the performance of multiplication but not subtraction, whereas holding an image in the mind delayed subtraction but not multiplication. This result indicates that arithmetic function is related to working memory in a subsystem-specific manner: multiplication is more closely linked to phonological loop and subtraction to visuo-spatial sketchpad. Whereas this is not compatible with the notion that arithmetic is done on a unitary, amodal representation of numbers, it provides support for the triple-code and/or the modular processing models on human numerical cognition in which number representations are specific for input/output modality and arithmetic types.