A recent study published in the journal Biological Psychiatry examined the impact of methylphenidate (a stimulant medication) and atomoxetine (a "non-stimulant") on a very specific cognitive skill. "Time discrimination" refers to our ability to estimate how long we have been engaged in a task and the ability to notice differences among temporal patterns.
Dr. Russell Barkley has highlighted tempo control differences for some time now, and the difference continues to be a point of reference in investigations of brain-based differences among folks with ADHD. In this 2003 study of time discrimination deficits, the authors conclude that these deficits have "cascaded effects on the temporal organization of behaviour in children and adolescents with ADHD..."
While time discrimination is a subtle distinction (perhaps differences of just milliseconds) identified in laboratory studies, those "cascaded effects" are the challenges which parents and teachers and spouses of adults with ADHD observe day to day: difficulty planning multi-step tasks, and problems arriving to events on-time, for example. These subtle differences may even be implicated in the impulsivity observed in some individuals with executive disorders.
Impact of medication
In this recent investigation by Anna Smith and her colleagues, both the stimulant and non-stimulant "normalized" activity in brain regions which were underactive in the ADHD sample, although only the stimulant agent demonstrated improved performances on behavioral measures of time discrimination.
Non-medication supports for time management
In addition to medication management of ADHD-related time challenges, other supports (check out the links to learn more and maybe experiment with these yourself) include: