Chronobiology internationalApr 7, 2012

Changing test times to match sleep habits affects daily thinking and behavior in young night owls and older morning people

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Updated Mar 25, 2026

Abstract

The synchrony effect is observed in median reaction times during a psychomotor vigilance task, even when testing aligns with individual sleep-wake preferences.

Older adults typically perform better in the morning, while younger adults tend to excel in the evening.
Testing at fixed times can introduce confounds like sleep pressure and circadian phase differences, which may influence performance.
Adaptation of testing times to individual sleep-wake schedules shows persistence of synchrony effects in median reaction times.
However, the synchrony effect appears weakened for incongruent trials on Stroop performance and for the slowest reaction times.
Variations in socio-professional timing, accumulated sleep need, and circadian phase may partially mediate the synchrony effect.

Simplified

The synchrony effect refers to the beneficial impact of temporal matching between the timing of cognitive task administration and preferred time-of-day for diurnal activity. Aging is often associated with an advance in sleep-wake timing and concomitant optimal performance levels in the morning. In contrast, young adults often perform better in the evening hours. So far, the synchrony effect has been tested at fixed clock times, neglecting the individual's sleep-wake schedule and thus introducing confounds, such as differences in accumulated sleep pressure or circadian phase, which may exacerbate synchrony effects. To probe this hypothesis, the authors tested older morning and young evening chronotypes with a psychomotor vigilance and a Stroop paradigm once at fixed morning and evening hours and once adapting testing time to their preferred sleep-wake schedule in a within-subject design. The authors observe a persistence of synchrony effects for overall median reaction times during a psychomotor vigilance task, even when testing time is adapted to the specific individual's sleep-wake schedule. However, data analysis also indicates that time-of-day modulations are weakened under those conditions for incongruent trials on Stroop performance and the slowest reaction times on the psychomotor vigilance task. The latter result suggests that the classically observed synchrony effect may be partially mediated by a series of parameters, such as differences in socio-professional timing constraints, the amount of accumulated sleep need, or circadian phase, all leading to differential arousal levels at testing.

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Changing test times to match sleep habits affects daily thinking and behavior in young night owls and older morning people

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