The Pursuit of Effective Working Memory Training: a Pre-registered Randomised Controlled Trial with a Novel Varied Training Protocol

Self-reported strategy use in working memory tasks

Mnemonic strategies can facilitate working memory performance, but our knowledge on strategy use as a function of task characteristics remains limited. We examined self-reported strategy use in several working memory tasks with pretest data from two large-scale online training experiments. A three-level measure of strategy sophistication (no strategy, maintenance, manipulation) was coded based on participants' open-ended strategy reports. A considerable portion of participants reported some memory strategy, and strategy sophistication was associated with objective task performance. We found a consistent effect of stimulus type: verbal stimuli (letters or digits) elicited higher strategy sophistication than nonverbal ones (colours or spatial positions). In contrast, the association between task paradigm and strategy sophistication was less consistent in the two experiments. The present results highlight the importance of self-generated strategies in understanding individual differences in working memory performance and the role of stimulus characteristics as one of the task-related determinants of strategy use.

Training allows switching from limited-capacity manipulations to large-capacity perceptual processing

In contrast to perceptual tasks, which enable concurrent processing of many stimuli, working memory (WM) tasks have a very small capacity, limiting cognitive skills. Training on WM tasks often yields substantial improvement, suggesting that training might increase the general WM capacity. To understand the underlying processes, we trained a test group with a newly designed tone manipulation WM task and a control group with a challenging perceptual task of pitch pattern discrimination. Functional magnetic resonance imaging (fMRI) scans confirmed that pretraining, manipulation was associated with a dorsal fronto-parietal WM network, while pitch comparison was associated with activation of ventral auditory regions. Training induced improvement in each group, which was limited to the trained task. Analyzing the behavior of the group trained with tone manipulation revealed that participants learned to replace active manipulation with a perceptual verification of the position of a single salient tone in the sequence presented as a tentative reply. Posttraining fMRI scans revealed modifications in ventral activation of both groups. Successful WMtrained participants learned to utilize auditory regions for the trained task. These observations suggest that the huge task-specific enhancement of WM capacity stems from a task-specific switch to perceptual routines, implemented in perceptual regions.