A study on how caffeine affects the brain’s left hemisphere has just been published by PLOS ONE, an open, interactive online science journal. Finally!
Both analyses, the signal detection approach and the mixed-effect logistic regression agreed in the fact that caffeine affects performance in the affective lexical decision task. It is evident that caffeine does not affect lexical decision performance in general, but in accordance with the initial hypotheses specific interactions with the emotional valence of the stimulus were observed.
This may explain the grumblings from your morning regulars, or why your espresso trainer friend is all cracked out. Way to go, science!