Related Experiment Video
Updated: Jan 6, 2026

Collecting Sleep, Circadian, Fatigue, and Performance Data in Complex Operational Environments
Published on: August 8, 2019
Daily fluctuations in sleep duration and quality affect next-day processing speed performance in young and older
Johanna Schwarz1,2, Malin Freidle1, Wessel van Leeuwen1
1Department of Psychology, Stockholm University, Stockholm, Sweden.
Study Objectives:
Knowledge about how day-to-day variations in sleep affect cognitive performance in real-world contexts is currently limited. This study investigated how daily fluctuations in sleep duration, efficiency, and quality affect next-day processing speed, and tested whether these associations differ between young and older adults.
Methods:
A total of 158 young (18-30 years) and 168 older adults (55-75 years) participated in a 21-day intensive longitudinal design. Sleep duration and efficiency were measured using actigraphy, while sleep quality was assessed via sleep diaries. Processing speed was measured using a 60 s smartphone-based Digit Symbol Substitution Task, administered up to eight times per day. Multilevel mixed models tested the within- and between-person effects of sleep duration, sleep efficiency and sleep quality, as well as the effect of age group on processing speed.
Results:
Within-person, a sleep duration shorter than their own average (p < .001), and a sleep quality poorer than their own average (p < .05) predicted poorer next-day performance. Between-person differences in sleep duration, sleep efficiency and sleep quality were not significantly associated with processing speed. Older adults showed worse performance than young adults (p < .001), but the effect of daily sleep fluctuations on performance did not significantly vary between age groups.
Conclusions:
Daily fluctuations in sleep duration and sleep quality are linked to processing speed in young and older adults in real-world contexts. Results suggest that within-person, day-to-day variations in sleep may be more important than between-person differences. Maintaining an adequate sleep duration each day may help prevent cognitive impairments in daily functioning across age groups.
Related Concept Videos
Insufficient Sleep and Sleep Deprivation
Sleep deprivation is a more severe form of sleep loss...
Understanding Sleep
The circadian rhythm, a nearly 24-hour cycle, is deeply influenced by environmental light cues. Light exposure directly affects the hypothalamus, which in turn regulates...
Substance Use Disorders Affecting Sleep
Understanding the concepts of physical dependence,...
Sleep-Wake Cycles
NREM Sleep
NREM sleep comprises four progressive stages that seamlessly merge:
Longitudinal Research
Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response
The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of...

