Working memory’s workload capacity

Strayer, David L.; Coleman, JR; Heathcote, Andrew · 2015 · Memory & Cognition

DOI: 10.3758/s13421-015-0526-2

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Summary

This study investigates the role of dual-task interference in working memory by applying workload capacity theory to a novel dual two-back task. The authors aimed to distinguish between dual-task interference (conflict between maintenance and manipulation operations) and proactive interference (conflict between trials). They utilized the "gatekeeper" task, a redundant-target dual n-back paradigm where participants monitor simultaneous auditory and visual streams and respond if either stimulus matches the item from two trials prior. This design allows for the application of Townsend and Nozawa’s workload capacity coefficient, which quantifies whether processing channels share limited resources. The study also assessed the reliability of this task and its correlation with complex-span measures, specifically the Operation Span (OSPAN) task. The experiment involved 311 undergraduate participants who completed the OSPAN task followed by the gatekeeper task. The gatekeeper task included single-task blocks (auditory or visual only) and dual-task blocks (both modalities). To control for response bias, participants were randomly assigned to conditions with either 50% or 75% target probabilities in dual blocks. Performance was measured via accuracy and response times (RTs). The authors employed Bayes factor analyses to evaluate model fit and effect sizes, providing robust statistical evidence for or against specific hypotheses regarding dual-task load and capacity limitations. Results indicated that dual-task demands significantly reduced both speed and accuracy compared to single-task conditions. Specifically, mean correct RTs were substantially slower in dual blocks than in single blocks, and sensitivity ($d'$) was lower in dual conditions. Crucially, the workload capacity analysis revealed that the performance decrement was mediated by the sharing of a limited amount of processing capacity, confirming that working memory operations are subject to capacity constraints similar to perceptual tasks. The gatekeeper task demonstrated high psychometric reliability, attributed to the use of small stimulus sets that induced constant, high levels of proactive interference. Furthermore, accuracy in the bias-minimized (50% target) version of the task showed stronger correlations with OSPAN scores than typically observed in standard n-back tasks, suggesting better convergent validity with complex-span measures. The findings provide a rigorous method for analyzing workload capacity in working memory, demonstrating that dual-task interference arises from limited processing capacity shared between modalities. The gatekeeper task offers a reliable and valid measure of working memory that effectively captures both storage and manipulation demands. By establishing a link between workload capacity coefficients and working memory performance, the study bridges systems factorial technology with cognitive psychology, offering a refined tool for assessing individual differences in information processing and multitasking capabilities.

Key finding

Working memory shows clear capacity sharing between simultaneously maintained auditory and visual two-back streams: the new redundant-target dual two-back yields formal Townsend-Nozawa workload-capacity coefficients indicating sub-unlimited capacity, more reliable performance metrics (due to deliberately-induced high proactive interference), and stronger convergent validity with complex-span measures than standard n-back paradigms — making it a candidate cognitive-load benchmark.

Methodology

lab_experiment

Sample size: N=311 (final sample after exclusions; 147 in 50% group, 164 in other).

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• dual task multitasking
• capacity resource theory
• cognitive capacity variation
• working memory
• workload measurement