The extent to which working memory training improves performance on untrained tasks is highly controversial. Here we address this controversy by testing the hypothesis that far transfer may depend on near transfer using mediation models in three separate randomized controlled trials (RCTs). In all three RCTs, totalling 460 individuals, performance on untrained N-back tasks (near transfer) mediated transfer to Matrix Reasoning (representing far transfer) despite the lack of an intervention effect in RCTs 2 and 3. Untrained N-back performance also mediated transfer to a working memory composite, which showed a significant intervention effect (RCT 3). These findings support a model of N-back training in which transfer to untrained N-back tasks gates further transfer (at least in the case of working memory at the construct level) and Matrix Reasoning. This model can help adjudicate between the many studies and meta-analyses of working memory training that have provided mixed results but have not examined the relationship between near and far transfer on an individual-differences level.
The potential that working memory (WM) training can transfer to untrained tasks that differ substantially from the training task (‘far transfer’) has generated substantial excitement with regard to better understanding the causal relationship between WM and related cognitive processes1,2,3,4,5,6, as well as to applied domains where such training can benefit health and well-being7,8,9,10. In particular, the effectiveness of WM training to improve fluid intelligence has been a controversial and highly debated topic, with some meta-analyses showing a small but significant positive effect on fluid intelligence11,12,13,14,15, while others argue that there is no evidence of generalization to fluid intelligence after training16,17. A difficulty in reconciling across different studies is that individual differences in performance and learning are ubiquitous in this literature and impact the average benefits18. Furthermore, training procedures and outcome measures differ greatly across studies, making meaningful comparisons challenging19.