Effect of time of day on arithmetic fact retrieval in a number-matching task.

The goal of this study is aimed to investigate a possible effect of time of day on arithmetic fact retrieval in a number-matching task. We tested 96 students (age range 19-33 years) at 9 a.m. and at 1 p.m., in a counterbalanced order. The subjective alertness levels were also recorded. As regards retrieval efficiency, the results showed that the sum interference effect was significantly more pronounced in the morning (9 a.m.) than at midday (1 p.m.). As expected, participants showed higher subjective alertness levels at 1 p.m. than at 9 a.m.. However, the difference of subjective alertness did not completely explain differences in interference at two testing sessions. The results could be explained with respect to the variation of working memory efficiency during the day.