The detrimental effect of interference in multiplication facts storing: typical development and individual differences.

The difficulty in memorizing arithmetic facts is a general and persistent hallmark of math learning disabilities. It has recently been suggested that hypersensitivity to interference could prevent a person from storing arithmetic facts. The similarity between arithmetic facts would provoke interference, and learners who are hypersensitive to interference would therefore encounter difficulties in storing arithmetic facts in long-term memory. In this study, we created a measure of the interference weight for each multiplication by measuring the overlap of digits between multiplications. First, we tested whether the interference parameter could predict performance across multiplications by analyzing the data from undergraduates published by Campbell (1997). The interference parameter substantially predicted performance across multiplications. Similarly, the performance across multiplications was substantially determined by the interference parameter in 3rd-grade children, 5th-grade children, and undergraduates we tested. Second, we tested whether people with poor arithmetic facts abilities were particularly sensitive to the interference parameter. We tested this hypothesis in typical development by analyzing the data from the 3rd-grade children, 5th-grade children, and undergraduates. We analyzed data with regard to atypical development from a published case study of dyscalculia as well as from 4th-grade children, with either poor or good multiplication skills, tested twice 1 year apart. Results showed that the individual sensitivity to the interference parameter determined part of the individual differences in multiplication performance in all data sets. These findings show that the learning of multiplications is particularly interference prone because of feature overlap and that people who are sensitive to this parameter therefore encounter difficulties in memorizing arithmetic facts.