In younger subjects (18 - 37 years), caffeine has been shown to improve performance during distraction, rather than during simple tasks. (coffeeandhealth.org)
It also seems to work on memory in healthy younger subjects, too. (marksdailyapple.com)
Similarly, Johnson et al. (1973) took muscle samples from 6 cadavers of younger subjects who died suddenly (aged 17 - 30 years). (strengthandconditioningresearch.com)