A small dose of caffeine not only perks you up, it also increases the speed and accuracy for recognizing positive words.
Researchers studied the effects that small doses of caffeine - equivalent to two or three cups of coffee - have on humans. They found having a little bit of caffeine thirty minutes before performing a task increases the recognition of positive words and has no effect on negative or neutral words.
Study authors suggest this effect is driven by caffeine's strong effects on dopamine in the language-dominated regions of the brain. Previous research has shown caffeine increases activity in the central nervous system.
And normal doses of the stimulant improve performance on simple cognitive tasks and behavioral responses.