Neurophysiological correlates of mental arithmetic

Thirteen subjects were extensively trained on nine multiplication problems varying in difficulty. Practice was associated with a reaction time speed up and an attenuation of the problem size effect. The introduction of previously unpracticed problems led to a performance rebound to pretraining levels, indicating practice specificity. The eventrelated potentials were characterized by a late positive complex, followed by a positive slow wave. Offset latency of positive slow wave and preresponse amplitude at parietal electrodes showed practice specificity effects that systematically changed with practice and problem size, indicating an association with the load imposed on working memory. The peak of the late positive complex probably reflects task learning or adaptation effects because it was attenuated by practice predominantly at frontal electrodes, showed no practice specificity, and was not affected by problem size.