Simultaneous and Sequential Presentations Differentially Modulate the Temporal Dynamics of Working Memory Processes

Working memory (WM) involves continuous and dynamic processes, including encoding, maintenance, and retrieval. While many studies have focused on the maintenance of WM information, encoding strategies also impact WM performance and can be shaped by the presentation format of stimuli. However, how presentation formats modulate neural responses across WM stages remains unclear. To address this issue, we conducted an EEG study examining the effects of presentation formats (simultaneous, location-sequential, and center-sequential presentation) and WM loads (one and three abstract shapes). Behavioral results showed longer RTs for the location-sequential than for the center-sequential format. Additionally, the recency effects observed in both sequential conditions reflect the influence of ordinal information. EEG results revealed distinct load-dependent alpha activity patterns across presentation formats during WM maintenance. Simultaneous presentations exhibited a persistent decrease in alpha power, whereas both sequential presentations exhibited an initial decrease followed by a subsequent increase. During sequential encoding, alpha power decreased cumulatively with each additional item in the location-sequential format, but not in the center-sequential format. At retrieval, the probe elicited a load-dependent negative potential (i.e., the N3rs) across all formats. The N3rs load modulation was stronger for simultaneous presentations than sequential ones and was more pronounced for earlier positions than for the last position in sequential presentations. In conclusion, our findings demonstrate that the spatial and temporal order information embedded in presentation formats modulates load-dependent neural responses across WM stages. These effects extend beyond maintenance to encoding and retrieval, highlighting the influence of presentation formats on WM neural dynamics.