Effects of caffeine on visual cognitive processing in humans: a systematic review of attentional and perceptual paradigms

Background: Caffeine is the world’s most widely consumed psychostimulant and can alter visual attention and perception. Previous reviews have largely pooled heterogeneous paradigms into broad behavioural domains, potentially obscuring task-specific effects. This systematic review examined acute caffeine effects across visual-attention and perceptual-processing tasks in healthy, rested adults. Methods: PubMed, Scopus and PsycINFO were searched from inception to June 2026. Eligible studies were randomised, double-blind, placebo-controlled parallel-group or crossover trials reporting at least one numerical behavioural outcome of visual cognition. Risk of bias was assessed using Cochrane RoB 2, and findings were synthesised narratively across four functional task families: rapid-response; vigilance and continuous-monitoring; conflict-control, orienting and set-shifting; and visual-search and perceptual-sensitivity paradigms. Results: Thirty-nine articles representing 40 studies and 1,744 participants were included, predominantly in young healthy adults, using crossover or parallel-group designs and acute caffeine doses ranging from 60–500 mg. Six studies were at high risk of bias, 33 had some concerns and one was low risk. Significant benefits occurred in 8/13 rapid-response and 8/18 vigilance studies, with vigilance additionally showing comparatively frequent improvements in target detection, accuracy and lapses. Although 9/22 conflict-control, orienting and set-shifting studies reported some benefit, only five showed process-specific improvement. Visual-search and perceptual-sensitivity evidence was limited, with benefits in 2/7 studies. Conclusion: Overall, caffeine appears to enhance attentional readiness, sustained engagement and rapid responding more consistently than interference control or perceptual sensitivity. Functional task demands may therefore explain caffeine responsiveness better than overall task complexity, supporting more task-specific evaluation of caffeine’s cognitive effects. This is a preprint and has not undergone peer review.