Is short-term storage correlated with fluid intelligence? Strategy use explains the apparent relationship between ‘number of remembered items’ and fluid intelligence

Working memory is a core cognitive system that actively maintains information in an accessible state to support a variety of everyday tasks. Crucially, working memory performance has frequently been shown to strongly correlate with fluid intelligence. Traditionally when these correlations have been observed, the working memory tasks involved required a high degree of manipulation and executive function, as opposed to solely utilizing short-term storage capacity. However, recent work has claimed that simple storage capacity is also correlated with fluid intelligence, and that this is driven by a particularly special and dissociable component of capacity, the ‘number of items represented’ (rather than the precision of those representations). These results have been used to argue that investigating the underlying mechanisms of capacity limitations may be critical to understanding aspects of fluid intelligence. Here we demonstrate that such correlations do not arise solely or primarily from simple storage capacity (nor a single dissociable component of capacity), but are driven by the availability of strategic encoding of different kinds of visual representations. Specifically, a working memory task that decreased the utility of storing and making use of spatial ensemble information, while holding constant the number of items to be remembered and the exact changes participants needed to detect, significantly reduced the correlation between working memory performance and fluid intelligence. Thus, despite being probed on the same items, with the same foils, at the same set size, only working memory displays that allowed for the strategic use of both item and ensemble representations correlated with fluid intelligence. These results provide evidence against the hypothesis that simple storage alone is related to fluid intelligence. They also demonstrate that participants make use of more complex and structured representations rather than solely individual item representation, and that strategic utilization of these representations is what correlates strongly with fluid intelligence.