Do functional components of working memory exhibit independent diurnal variations under semi-ecological conditions? Evidence from a time-of-day protocol

Working memory (WM) is a cognitive system comprising multiple components, including simultaneous storage and processing of information, updating mental representations, and binding elements into coherent structures. While various studies investigated whether WM performance varies throughout the day, their findings are inconsistent. These discrepancies have been partly attributed to methodological differences, such as variations in participant chronotypes and experimental protocols. Some evidence suggested that WM components may exhibit independent diurnal variations and thus may also contribute to these inconsistent findings. Considering this, we examined whether tasks targeting distinct WM dimensions present independent diurnal fluctuations. Participants completed complex spans, updating, and binding tasks at different time-of-day (ToD): morning, midday, afternoon, and evening. A composite score was also computed to evaluate ToD effects on general WM performance. Our findings indicated that not all aspects of WM are equally affected by ToD: tasks involving simultaneous processing and storage, particularly within the visuospatial domain, showed greater diurnal variability than updating and binding tasks. Composite RTs were faster in the morning. These findings imply that task selection could have contributed to the mixed results in prior research. Future investigations should consider using multiple paradigms targeting diverse WM dimensions to better understand how ToD influences WM performance.