Final answer:
Cognitive differences in caffeine studies are primarily due to variations in caffeine metabolism, though participants' arousal levels and experimental design can also influence the results.
Step-by-step explanation:
Differences in cognitive results from caffeine experiments are likely attributed to B) Differences in caffeine metabolism. Caffeine is a stimulant that affects various systems within the body, including the central nervous system. Its effect on cognitive functions, such as alertness and fatigue suppression, is due to its interaction with adenosine receptors in the brain, blocking the onset of drowsiness caused by adenosine. However, the metabolism of caffeine varies among individuals which affects the duration and magnitude of its effects. Factors such as genetic differences in the enzymes responsible for caffeine breakdown, body mass, age, and tolerance levels contribute to this variation. Caffeine metabolism influences how long the drug stays active within the system and therefore, how it impacts cognitive performance in tasks such as reaction time, vigilance, and the ability to process information.
Other potential influences not explicitly stated in the options but worth considering include Participants' arousal levels and the Experimental design, as these can also introduce variability in cognitive outcomes of caffeine consumption studies. Participants' baseline arousal could interact with the effects of caffeine, and the experimental design, including control and precision in measuring outcomes, can greatly influence the results.