Figure 3. Double dissociation in stimulation and cognitive training outcomes: combined tDCS and cognitive training is more beneficial for low achievers, while cognitive training alone is more beneficial for high achievers.

(a) Pearson and (b) Spearman correlational analyses showing the modulatory effects of baseline mathematics achievement and levels completed at the end of the training. The data on panel A reflects residuals after partialling out the correlation with the performance on the first day of training. One participant from the sham group was excluded for underperforming by 2.5 SD from the mean. Note that some data points on B panel are overlapping and therefore less data points appear.