The study investigated three main areas of cognition; 1) verbal memory, 2) motor skill acquisition and 3) perceptual learning.
1) Verbal memory - two verbal memory tasks were administered to all groups of participants, shortly after the tasks there were interventions. 7 Hours later the participants were tested on the verbal memory tasks and the results showed that the "nap" group performed significantly higher in this when compared to the caffeine and placebo group.
2) Motor learning - On this task it was the placebo group who out performed all others - the results in this task were infact quite varied in that the caffeine group appear to have been incredibly impaired. See image below.
3) Perceptual learning - Napping & Caffeine produced high perceptual learning compared to the placebo group.
Interested in reading more? The full PDF can be found here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2603066/pdf/nihms65981.pdf