Contributions from Long-Term Memory Explain Superior Visual Working Memory Performance with Meaningful Objects

Abstract Visual working memory (WM) capacity has been claimed to be larger for meaningful objects than for simple features, possibly because richer semantic representations enhance the distinctiveness of stored items. However, prior demonstrations typically compared trial-unique meaningful objects with a small set of repeated simple features. This design confounds meaningfulness with proactive interference (PI), such that PI is minimal for trial-unique objects but substantial for repeated features. As a result, superior performance for meaningful objects may reflect contributions from episodic long-term memory (LTM) rather than expanded WM capacity. To test this, Experiment 1 measured WM for repeated colors, repeated meaningful objects, and trial-unique meaningful objects. The advantage for objects over colors was replicated in the trial-unique condition, but eliminated for repeated objects that equated PI across stimulus types. Hierarchical Bayesian dual-process modeling revealed that the trial-unique advantage reflected stronger familiarity signals, whereas recollection remained stable across stimulus types. Experiment 2 assessed WM storage directly using contralateral delay activity (CDA), an electrophysiological marker of the number of items stored. Although trial-unique objects again yielded behavioral advantages, CDA activity across increasing set sizes revealed a common slope and plateau for trial-unique meaningful objects and repeated colors. The CDA difference between stimulus types was additive and did not vary with set size, providing no evidence for an increased number of stored items. These findings demonstrate that previously reported advantages for meaningful objects primarily reflect reduced PI and enhanced LTM familiarity. When PI is equated, WM storage limits for simple and meaningful stimuli are equivalent. Significance Statement Working memory provides the mental workspace that underlies reasoning, learning, and everyday decision making, yet its capacity is sharply limited. Previous studies suggested that meaningful, real-world objects are remembered better, raising the possibility that knowledge can expand this known capacity limit. However, many designs confound working memory with long-term familiarity. Here, equating proactive interference removed the behavioral advantage for meaningful items. A neural marker of active storage showed additive differences between stimulus types that did not vary with load, indicating no increase in the number of stored items. These findings identify interference, rather than expanded storage, as the source of the reported advantage and offer practical guidance for future experimental design and theories of memory limits.