Abstract: There are two different theories, the retrieval and nonretrieval theories, accounting for the mechanism of the problem-size effect. The retrieval theories indicated that the problem size effect is attributed to various aspects of the representation of stored arithmetic knowledge. Recently, the researchers pay much more attention to the important role of nonretrieval procedures such as counting and decomposition in the problem size effect. The less efficient retrieval and calculation strategies and more use of nonretrieval procedures contribute to the problem size effect. Due to the different proportion of various strategies, the problem size effect in addition and subtraction shows distinct forms. Future research seems to consider various different study means (e.g., combined ERP and fMRI) and unify the standards to classify the small and large problems

Key words: problem-size effect, procedural strategy, addition, subtraction