Capacity limit of attention and visual short-term memory dissociates from cognitive aptitude
The relationship between attention, VSTM and intelligence is a matter of intense debate. Using neuroimaging, we found that VSTM & attention share dependence on a posterior parietal region, which demonstrates a response that increases with the number of items up to a capacity limit of around four items, but then plateaus. We suggest it plays an important role in both attention & memory tasks and is responsible for the creation or maintenance of a limited number of distinct object representations. But, then, what is the relationship between this capacity limit and aptitude? It has been claimed that this capacity reflects a fundamental limit on the ability to process multiple items at once, and is a strong predictor of intelligence. We conducted an individual differences study (N=64) with three independent measures of VSTM and one of general intelligence. We found that the least noisy, most simply interpretable and highest estimate of VSTM (from whole report) does not correlate with intelligence. However, other measures (using the sample probe method) appear to be contaminated by the influence of other cognitive requirements (perhaps manipulation or strategy) that disrupt performance at higher set sizes, and do correlate with intelligence. We conclude that attention & VSTM share a capacity-limited component, but this capacity is not tightly related to cognitive aptitude.