A controlled experiment found improved information processing after d-amphetamine without a corresponding improvement in response inhibition. Handling a faster stream of information and stopping an initiated action were separable abilities.
Fillmore and colleagues studied 22 healthy adults without reported illicit-stimulant use or drug dependence. A randomized double-blind within-subject design compared placebo with 7.5 and 15 mg per 70 kg d-amphetamine. A rapid-information-processing task adjusted presentation speed according to performance, while a stop-signal task separately assessed inhibitory control. Drug effects were assessed at multiple times and with repeated testing.
Information-processing rate improved in a dose-dependent pattern. The tested doses did not establish enhanced response inhibition. The processing task was not simply a button-speed test: correct performance allowed the information stream to become faster, while errors and omissions slowed it. Its benefit therefore concerns performance under that adaptive task design, not an automatic improvement in every higher-level cognitive function.
The selected healthy sample and limited doses constrain generalization to ADHD, dependence, sleep deprivation or mixed drug exposure. The study’s physiological and subjective effects also do not replace the negative inhibition result. A favorable effect on one task cannot establish better impulse control during a real-world event. Conversely, the absence of an inhibition benefit does not negate the demonstrated processing effect. This dissociation is useful when assessing broad stimulant-enhancement claims: the task, endpoint and timing should be named, and an improvement in processing should not be substituted for evidence about stopping, judgment or safe driving.
See post-error adaptation in a different observational population.