Electrophysiological correlates of list-length and delay effects in visual recognition memory

The amount of information in episodic memory (list length) and the time delay between study and retrieval, including serial position at the beginning (primacy) or at the end (recency) of the list, are among the most prominent determinants of subsequent retrieval success. Although both types of factors are central to theories of memory, they are often confounded in experimental designs, making it difficult to determine whether list-length effects reflect genuine interference from storing more items or time-related processes such as decay. Here, we used electroencephalography (EEG) to examine time-resolved neural signatures of visual recognition memory as a function of list length and delay, focusing on event-related potential (ERP) old/new effects and multivariate EEG decoding. Across two experiments, we observed robust list-length effects on the frontal (FN400) and parietal (LPC) ERP old/new components, as well as on decodability of old and new items. Critically, Experiment 2 employed a delay-controlled design and demonstrated that list-length effects persist when study–test delay is controlled ruling out explanations based on recency confounds. However, serial position modulated neural signals independently producing a primacy advantage that was more prominent in frontal activity. This resulted in dissociable neural signatures: a parietal component selectively sensitive to list length and a frontal component selectively sensitive to primacy. These findings show that list length and delay exert separable influences on neural markers of recognition memory and support the view that list-length and temporal factors (delay and serial position) work via different memory mechanisms.