A central capacity limit to the simultaneous storage of visual and auditory arrays in working memory.

Cowan, Nelson · 2007 · OpenAlex

DOI: 10.1037/0096-3445.136.4.663

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Summary

This study investigates whether working memory (WM) is constrained by a central capacity limit shared across sensory modalities or by independent, modality-specific stores. Motivated by Cowan’s theory that the focus of attention holds approximately four items regardless of modality, the authors tested if simultaneous storage of visual and auditory information competes for this central resource. Previous research suggested interference between visual and verbal tasks, but often allowed for rehearsal strategies that might bypass central limits. This study aimed to eliminate such strategies to isolate central capacity constraints. The researchers conducted five experiments using a change-detection paradigm. Participants viewed visual arrays of colored squares and simultaneously heard auditory arrays of digits spoken from four spatially separated loudspeakers. In unimodal conditions, participants attended to only one modality; in bimodal conditions, they attended to both. To prevent covert verbal rehearsal of the auditory stimuli, Experiments 3–5 employed post-perceptual masks that disrupted modality-specific temporary storage. Capacity ($k$) was calculated using the formula $k = I[p(hits) - p(false alarms)]$, where $I$ is the number of items. This method quantifies the number of items retained in WM independent of guessing. Results from Experiments 1 and 2 showed dual-task tradeoffs for visual capacity but not auditory capacity, suggesting auditory memory benefited from passive storage or rehearsal. However, when masks eliminated these auxiliary supports in Experiments 3–5, significant dual-task costs emerged for both modalities. Crucially, the total number of items remembered in bimodal conditions did not exceed the higher of the unimodal capacities (approximately 3–4 items). For instance, visual capacity dropped from roughly 3.6 items in unimodal conditions to 2.5–2.7 items in bimodal conditions when masks were present. The sum of visual and auditory items stored simultaneously was constrained by the same limit as single-modality storage. These findings support the existence of a central capacity limit in working memory, likely corresponding to the focus of attention, which governs the simultaneous storage of information across different sensory modalities. The data indicate that while modality-specific passive storage exists, it does not expand the total number of items that can be actively maintained in WM. Instead, visual and auditory arrays compete for the same central resource, reinforcing the view that WM capacity is defined by a general, limited-capacity mechanism rather than independent buffers for each sense.

Key finding

When passive storage was eliminated, the total number of visual and auditory items remembered simultaneously did not exceed the capacity of the higher unimodal modality, supporting a central capacity limit of approximately three to four items.

Methodology

lab_experiment

Sample size: 24

Provenance

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

Topics

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• working memory