Drug-related images can change how a person selects a response even when average response speed does not distinguish the groups. A 2026 methamphetamine study found a cue-specific pattern of interference, rather than a simple across-the-board slowing.
Xu and colleagues used a modified Simon task in people with methamphetamine use disorder and healthy controls. An image appeared on one side of the screen, but participants had to choose a response according to its surrounding frame color. Image location could automatically favor the same-side hand, creating conflict when the instructed answer required the opposite hand.
The image could depict a drug cue or a neutral cue. This design asks whether learned associations with a drug image change competition between an automatic response and the task-required response. It is a human behavioral comparison, not an experiment administering methamphetamine.
In the methamphetamine group, drug cues produced a larger Simon effect than neutral cues. The controls did not show that cue-related difference. The methamphetamine group also showed conflict adaptation for neutral cues but not drug cues: preceding conflict helped reduce later interference in one context, but not the other.
The main effect of group on reaction time was not significant. Consequently, describing the participants simply as slower would miss the study’s central result. The relevant evidence concerns how cue type and response conflict interacted.
The small sample limits estimates of individual differences. The authors also identified insufficient control of image characteristics and the absence of participants’ ratings of whether drug cues were rewarding or aversive. Smoking and alcohol differences were addressed after the fact rather than controlled in advance. Those limitations matter when assigning a psychological mechanism to a difference in task performance.
A response-conflict result cannot identify recent drug ingestion, establish a blood concentration, or diagnose impairment in a particular driver. Its value is showing why an average score can conceal context-dependent behavior. Driving requires different tasks and evidence, as explained in our controlled simulator study analysis.