Which "working memory" are we talking about? Complex span tasks versus N-back

Psychologists and neuroscientists often use complex span tasks or the n-back to measure working memory capacity. At first glance, both tasks require many cognitive processes attributed to the construct, including the maintenance of information amidst interference. Nevertheless, evidence for their convergent validity is mixed. This poses consequences for the interpretation of working memory performance in cognitive neuroscience, developmental psychology, applied psychology, and executive functioning research. We recruited a large and diverse sample using a multisite approach (N = 1,272; community and university participants) and had them complete multiple working memory capacity, updating, and fluid intelligence tests. We found strong evidence for a dissociation between complex span and n-back tests, and more broadly, between working memory capacity and updating factors. Observed correlations between complex span and n-back performance were modest (r̄ = .25), and at the latent level, the two factors only shared 20% of their variance. Each explained unique variance in fluid intelligence, and each was more strongly related to fluid intelligence than to each other, with updating measures demonstrating stronger relations to fluid intelligence. These results were interpreted via the disengagement hypothesis. What distinguishes updating measures from working memory capacity measures is their relative emphasis on disengagement from outdated information; disengagement drives their strong relation with fluid intelligence because problem-solving requires generating hypotheses but also discarding those discovered to be false. We suggest that researchers who want to measure and draw conclusions about working memory capacity or updating should not use complex span tasks and the n-back interchangeably.