Spatial statistical learning of task relevance, rather than stimulus prevalence, improves visual working memory recall

Our visual environment provides us with more information than we can process. Processing efficiency may be enhanced by leveraging inherent regularities in the environment, such as prioritizing likely target objects over unlikely ones. Although there is evidence that statistical learning improves visual working memory performance, it is unclear whether this improvement occurs through stimulus prevalence (how likely we are to encounter stimuli) or task relevance (how likely we are to use these stimuli). To distinguish between these two hypotheses, we examined whether frequent appearance, or frequent probing of stimuli (or both) improves visual working memory recall. Participants were asked to recall and replicate the orientation of one of two previously presented oriented gratings (Gabors) as precisely as possible. In two experiments, we manipulated (1) stimulus prevalence by presenting Gabors more frequently on one side (either left or right), and (2) task relevance by probing Gabors more frequently on one side (either left or right). We found comparable orientation recall performance for stimuli appearing at probable versus improbable locations, suggesting that regularities in stimulus prevalence do not improve memory recall. Contrastingly, we found better recall for stimuli appearing at locations that were more (versus less) likely to be probed. Specifically, task relevance enhanced recall performance, both by reducing the number of categorical errors and by increasing fine-grained recall precision. These findings demonstrate that statistical learning of task relevance, but not of stimulus prevalence, enhances visual working memory recall performance.