Time-of-day variations of indicators of attention: Performance, physiologic parameters, and self-assessment of sleepiness

Background: A study was performed to analyze time-of-day variations of diff erent indicators of attention and their interrelations. Methods: After a sufficiently long all-night sleep 12 healthy non-sleep-dep rived subjects ran through a test battery (Stanford Sleepiness Scale, Visua l Analogue Scale, Critical Flicker Fusion Test [CFF], Visualization Test Nu mber Facility Test, Reaction Time, Pupillometry, and modified Multiple Slee p Latency Test) every 2 hours from 7:00 AM until 11:00 PM, Time-of-day vari ations were tested nonparametrically with Friedman's test for repeated meas urements. Principal component factor analysis (of individually standardized values) was used to identify variable complexes with the same pattern of t ime-of-day variation. Results: Statistically significant time-of-day variations were found for al l variables, except for Fusion Frequency in CFF and Reaction Time. In facto r analysis the physiologic parameters (pupillometric variables and sleep la tencies) load on one factor, whereas the self-assessment scales, the Visual ization Test, Number Facilty Test, and CFF load on the second factor, The v ariables that load primarily on factor I show peak levels of alertness imme diately after getting up (at 7:00 AM) and again at 9:00 PM. Those variables that load primarily on factor 2 indicate a peak level of alertness around noon (11:00 AM-3:00 PM). Conclusions: Different aspects of attention follow different time-of-day va riations. It is discussed that these findings cart be attributed to underly ing circadian and homeostatic factors. (C) 2000 Society of Biological Psych iatry.