Individual differences reveal limited mixed-category effects during a visual working memory task

Abstract

Using stimuli from different categories may expand the capacity limits of working memory (WM) by spreading item representations across distinct neural populations. We explored this mixed-category benefit by correlating individuals’ behavioral performance with fMRI measures of category information during uniform- and mixed-category trials. Behaviorally, we found weak evidence for a mixed-category benefit at the group-level, although there was a high degree of individual variability. To test whether distinct neural patterns elicited superior performance in some individuals, we correlated a multivariate measure of neural category information with multiple behavioral metrics. This revealed a widespread positive relationship, intuitive for hit rate and working memory capacity, but counterintuitive for false alarm rate. Overall, these data suggest that mixed-category effects may support working memory performance, but unexpectedly, not all participants show this benefit. Only some people may be able to take advantage of representing mixed-category information in a differentiable way.