Hemispheric efficiency during the day: the influence of circadian preference and time-of-day on verbal and visuospatial tasks.

INTRODUCTION: Cognitive performance fluctuates daily due to the interaction between circadian and homeostatic processes, which may differently activate the two hemispheres. This study investigated the effects of time-of-day, circadian typology, and the synchrony effect on semantic categorization and visuospatial processing tasks with potential hemispheric lateralization. METHODS: A sample of 113 healthy young women (20.60 ± 2.60 years) performed two divided visual field tasks (semantic categorization and vertical landmark) in morning (08:00) and early afternoon (13:00) sessions. RESULTS: In the semantic task, an interaction between circadian preference and spatial position showed a progressive shift toward a right-visual-field preference from morning- to evening-types. A triple interaction (typology × word dominance × response type) revealed that for yes- responses, extreme chronotypes were faster with high-dominance items, while intermediate-types were faster with low-dominance ones. For no-responses, intermediate and evening-types favored low-dominance items, whereas morning-types showed no difference. In the landmark task, a Time-of-Day × Position interaction showed a right-visual-field advantage in the morning, which shifted to a left-visual-field advantage in the afternoon. DISCUSSION: Overall, findings indirectly suggest daily hemispheric variations based on task demands, with the left hemisphere more active in the morning and the right in the afternoon, and a modulation of circadian preference, at least for semantic processing.