How do working memory (WM) and episodic long-term memory (eLTM) interact to support immediate memory performance? Their contributions are often intertwined, reflecting a functional overlap that challenges clear-cut distinctions between the two systems. The present study investigates this interaction by assessing the combined effects of two diagnostic manipulations—proactive interference (PI) and secondary task effects (via Brown-Peterson-style filled retention intervals)—on binding tasks across varying set sizes. In Experiment 1, participants encoded word-object pairs and completed a four-alternative forced-choice test. Experiment 2 extended this paradigm to the visual domain, using object–color pairings tested via a continuous color reproduction task. In both experiments, PI selectively impaired performance at larger set sizes, consistent with increasing reliance on eLTM under higher memory load. Secondary task effects were strongest at smaller set sizes, reflecting a strong contribution of WM to performance. Secondary task effects impaired performance more strongly under high PI, especially at larger set sizes. This pattern suggests that when interference limits access to eLTM, participants shift reliance to WM—which, in turn, is vulnerable to disruption. These findings support a dynamic view in which WM and eLTM jointly contribute to immediate memory, with their relative involvement modulated by memory load and interference.
