Former methamphetamine users responded more slowly on a flanker task, but did not show larger conflict or sequential-adjustment effects than matched controls. General slowing and impaired conflict resolution were different findings in this experiment.
Bensmann and colleagues compared 24 abstinent former users with 24 individually matched controls in a cross-sectional human study. Former users averaged about 2.7 years of abstinence and approximately 7.2 years of prior consumption. A flanker task required selecting a response despite distracting competing information. Researchers also examined how the previous trial affected current performance and how people slowed after errors.
Former users had significantly longer overall reaction times. The groups did not differ significantly in flanker effects, Gratton effects or post-error slowing. Complementary Bayesian analyses supported the absence of the specified group effects. These analyses provide more information than simply declaring an ordinary nonsignificant test, but remain tied to the task, sample and statistical models.
A global label such as executive impairment can hide different processes. A slower response does not necessarily imply a larger cost of conflicting information or an inability to adjust after errors. Conversely, preserved task-specific effects do not establish normal performance in every other executive domain. This was neither acute dosing nor a repeated assessment of each participant through recovery. Selection into prolonged abstinence and differences in life history limit causal interpretation. The study does not establish that abstinence caused normalization or that a particular person is safe to drive. It supplies no blood, urine or oral-fluid threshold. A forensic opinion should identify whether the disputed function is response speed, conflict selection, error processing or another ability and use evidence matched to that function.
For a separate example of the limits of use-history comparisons, see our current-user driving study. The design and measured outcome determine which conclusions can be carried into an individual case.
Original investigation: doi:10.3389/fpsyt.2019.00823.