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In the Stroop task, which measures reaction time, improved accuracy was observed in subjects who believed they had ingested caffeinated coffee, even if they had only consumed decaf. Subjects who received caffeine and were told they were drinking decaf did not show an improved reaction time. Likewise, in a measure of reward motivation, the Card Arranging Reward Responsivity Objective Test, the participants who believed they had consumed caffeine sorted the cards more quickly than those who believed they’d consumed decaf. - www.newyorker.com