T T Brunye et al, 2011. Caffeine enhances real-world language processing: evidence from a proof-reading task. Journal of Experimental Psychology, Article in Press.

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Caffeine has become the most prevalently consumed psychostimulant in the world, but its influences on daily real-world functioning are relatively unknown. The present work investigated the effects of caffeine (0mg, 100mg, 200mg, 400mg) on a commonplace language task that required readers to identify and correct four error types in extended discourse: simple local errors (misspelling 1-2 syllable words), complex local errors (misspelling 3-5 syllable words), simple global errors (incorrect homophones), and complex global errors (incorrect subject-verb agreement, and verb tense). In two placebo-controlled, double-blind studies using repeatedmeasures designs, we found higher detection and repair rates for complex global errors, asymptoting at 200 mg in low consumers (Experiment 1) and peaking at 400 mg in high consumers (Experiment 2). In both cases, covariate analyses demonstrated that arousal state mediated the relationship between caffeine consumption and the detection and repair of complex global errors. Detection and repair rates for the other three error types were not affected by caffeine consumption. Taken together, we demonstrate that caffeine has differential effects on error detection and repair as a function of dose and error type, and this relationship is closely tied to caffeine’s effects on subjective arousal state. These results support the notion that central nervous system stimulants may enhance global processing of language-based materials, and suggest that such effects may originate in caffeine-related right hemisphere brain processes. Implications for understanding the relationships between caffeine consumption and real-world cognitive functioning are discussed.

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