Is Caffeine a Cognitive Enhancer?
www.gwern.net/docs/nootropics/2010-nehlig.pdf
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Two general mechanisms may account for most of the observed effects of caffeine on performance: (1) an indirect, non specific ‘arousal’ or ‘processing resources’ factor, presumably explaining why the effects of caffeine are generally most pronounced when task performance is sustained or degraded under suboptimal conditions; and (2) a more direct and specific ‘perceptual-motor’ speed or efficiency factor that may explain why, under optimal conditions, some aspects of human performance and information processing, in particular those related to sensation, perception, motor preparation, and execution, are more sensitive to caffeine effects than those related to cognition, memory, and learning. See also Smith 2005‘s caffeine led to a more positive mood and improved performance on a number of tasks. Different effects of caffeine were seen depending on the person’s level of arousal. Linear effects of caffeine dose were also observed. This is evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative effects of a long period of caffeine abstinence.