Daily fluctuations in children’s working memory accuracy and precision: Variability at multiple time scales and links to daily sleep behavior and fluid intelligence

Abstract

Children often experience better and worse days when performing cognitive tasks. Whether such fluctuations are systematic and how they are linked to fluctuations at faster time scales within days is less clear. To fill these gaps, we probed N = 108 fifth graders on WM tasks twice daily in morning and afternoon sessions, and also assessed nightly sleep behavior, over a period of four weeks using ambulatory assessment. Children systematically fluctuated in their recall of visuospatial and numerical information in WM across multiple time scales. These fluctuations showed consistencies but also discrepancies among each other. Especially, fast variability of memory precision across moments was related to load and fluid intelligence. Daily WM accuracy was positively coupled to sleep quality, but only in a subset of children with larger daily WM fluctuations. We propose that short-term WM fluctuations and their couplings to other time-varying constructs could help to explain long-term cognitive development. • Children show systematic intra-individual working memory (WM) fluctuations. • WM load particularly affected the rapid item-to-item variability of recall precision. • Lower momentary recall variability was linked to higher levels in fluid intelligence. • Nightly sleep quality predicted higher daily WM accuracy, but only in a subset of children. • These dynamics emphasize a nuanced distinction of faster and slower WM variability.