Grabner, R. H. 1 & De Smet, B. 2
1 Institute for Behavioral Sciences, Swiss Federal Institute of Technology, Zurich, Switzerland
2 Department of Educational Sciences, Katholieke Universiteit Leuven, Belgium
There is a long tradition of behavioral research showing that arithmetic problems are solved with various strategies including the retrieval of the correct solution from memory (fact retrieval) and the application of procedural strategies (e.g., transformation or counting). The applied strategies can be inferred from the size of the presented problems (e.g., small problems are frequently solved by fact retrieval) or can be directly assessed by means of trial-by-trial verbal strategy self-reports. However, the validity of these verbal strategy self-reports has been repeatedly questioned, and most investigations on the neural correlates of these strategies rely on the problem size rather than the strategy report approach. In the presented electroencephalography (EEG) study, we investigated the validity of both approaches by evaluating their association with the brain responses during mental arithmetic. To this end, 19 adults had to solve small and large addition and subtraction problems and to indicate the applied strategy (fact retrieval vs. procedure use) after each problem by means of verbal strategy reports. Analysis of event-related (de-)synchronization (ERD/ERS), a measure of task-related changes in oscillatory EEG activity, revealed a general convergence of verbal strategy reports and the problem size approach. Fact retrieval was accompanied by higher left-hemispheric theta ERS, while procedural strategies were reflected in higher widespread ERD in the lower alpha band and bilateral parietooccipital ERD in the upper alpha band. A direct comparison of the EEG data from both approaches showed a stronger association of the ERS/ERD data with the verbal strategy self-reports than with problem size. These findings suggest a higher sensitivity of verbal strategy self-reports to arithmetic strategies and thus provide the first neurophysiological evidence for the validity of verbal strategy self-reports.