I don't see anything that backs up the claim you made in that paper. The closest thing I see:
"Stimulant drugs do improve the ability (even without ADHD) to focus and pay attention. One function, which is reliably improved by stimulant medications, is sustained attention, or vigilance. Stimulants improve sustained, focused attention, but “selective attention” and “distractibility” may be worsened, possibly because of a drug induced increase in impulsivity."
fair enough -- i was basing it on my memory of a documentary I saw once -- i looked up the documentary but could not find a list of the studies it cited, so I Googled for studies on the question
"Stimulant drugs do improve the ability (even without ADHD) to focus and pay attention. One function, which is reliably improved by stimulant medications, is sustained attention, or vigilance. Stimulants improve sustained, focused attention, but “selective attention” and “distractibility” may be worsened, possibly because of a drug induced increase in impulsivity."
And that seems to contradict your point.