Individual Differences in Working Memory Capacity and What They Tell Us About Controlled Attention, General Fluid Intelligence, and Functions of the Prefrontal Cortex

Engle, Randall W.; Kane, Michael J.; Tuholski, Stephen W. · 1999 · OpenAlex

DOI: 10.1017/cbo9781139174909.007

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Summary

This paper addresses the nature of individual differences in working memory capacity (WMC) and their relationship to controlled attention, general fluid intelligence ($g_F$), and prefrontal cortex function. The authors argue that WMC is not merely a storage mechanism but reflects the capacity of a domain-free, limited-capacity controlled attention system. This system is responsible for maintaining temporary goals, suppressing distractions, and resolving conflicts. The central research question is whether WMC measures tap into this controlled processing capability and if this capability underlies higher-order cognitive functions and fluid intelligence. To investigate this, the authors employed a combination of regression studies, structural equation modeling, and experimental designs using extreme groups (high vs. low WMC). They distinguished between short-term memory (STM) tasks, which rely on simple storage, and complex working memory tasks (e.g., reading span, operation span), which require simultaneous processing and storage. In a key study involving 133 subjects, confirmatory factor analysis demonstrated that a two-factor model (separating STM and WM) fit the data significantly better than a single-factor model. Crucially, after partialing out variance common to both constructs, the residual WM variance (representing controlled attention) showed a strong, significant correlation with $g_F$ (measured by Raven’s and Cattell tests), whereas the STM residual did not. Further experiments ruled out alternative explanations, such as processing efficiency or skill-based trade-offs. By equating the difficulty of the processing component in operation span tasks across subjects, the authors found that the correlation between WMC and reading comprehension remained robust, indicating that the relationship is not driven by specific procedural skills. Additionally, a speeded-counting study revealed that high and low WMC individuals performed similarly on automatic subitizing (1–3 items) but differed significantly in counting time for larger sets (4–12 items), which requires controlled attention to track counted items. This controlled counting slope correlated with both WMC and $g_F$. Longitudinal studies with young children further supported these findings, showing that early WMC scores predicted later listening comprehension and inhibitory control (Stroop-like tasks), while comprehension did not predict later WMC. The significance of these findings lies in the conclusion that individual differences in WMC are isomorphic with differences in the capacity for controlled processing, mediated by the dorsolateral prefrontal cortex. The authors assert that WMC is a fundamental, abiding characteristic that predicts performance in higher-order cognition, fluid intelligence, and the ability to manage interference. This framework separates the construct of working memory from simple short-term storage, positioning controlled attention as the critical mechanism linking memory capacity to general intellectual ability.

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Topics

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• working memory
• cognitive capacity variation
• capacity resource theory