EVIDENCE LIBRARY
Can Beliefs About Self-Control Change Alcohol’s Effect on a Stop-Signal Test?
Two experiments separated beliefs, drinking behavior and laboratory stopping ability. A reassuring message did not reduce subsequent drinking and did not protect stop-signal performance.
Beliefs may influence some laboratory alcohol effects, but reassurance about self-control did not establish protection. In two experiments, manipulating participants’ beliefs did not significantly reduce craving or subsequent drinking. In the second experiment, the group given a reassuring message showed a greater alcohol-related slowing of stopping.
What the two experiments changed
Knibb and colleagues studied 81 participants in the first experiment and 82 in the second. Both used alcohol and placebo sessions, with beverage order counterbalanced. Participants were social drinkers recruited around a university, and testing took place in a laboratory furnished like a bar.
The alcohol dose was 0.5 grams per kilogram of body weight, mixed with lemonade. The placebo was lemonade with a vodka mist on the glass and drink surface. Beverage administration was single blind.
In the first experiment, participants received fabricated feedback after a stop-signal task, describing their self-control as high or average. The manipulation check did not confirm that this changed their beliefs about controlling drinking. That failure limits what the experiment can say about successfully changing such beliefs.
In the second experiment, a message delivered before drinking claimed that a small alcohol dose reduces the urge to drink. The comparison group received neutral information. This was an experimental manipulation, not an established scientific fact or advice to drink.
The reassuring message did not improve stopping
The stop-signal task required a quick keyboard response to an arrow, except when a tone instructed the participant to stop. Stop-signal reaction time estimated the time needed to cancel the response; it was not braking distance or a roadside sobriety score.
In experiment two, the drink-by-message interaction was significant, p = .017. In the reassuring-message group, mean stopping time was approximately 247 milliseconds after alcohol versus 217 after placebo. The neutral-message group did not show a significant alcohol-placebo difference in that measure.
Alcohol also increased inhibition errors overall in experiment two, regardless of message. Ordinary go-response times did not show significant drink or message effects. Stopping latency, stopping errors and response speed therefore gave different information.
Drinking outcomes did not follow the same pattern
Neither experiment found a significant effect of the belief manipulation on craving or freely consumed beer in a taste test. The first experiment found more beer consumed after the alcohol prime than after placebo; the second did not replicate that consumption difference.
This pattern does not support a simple chain in which a measured stopping deficit necessarily causes more drinking. Nor does it show that a message promising control prevents alcohol-related behavioral change.
The authors suggested that reassurance might reduce compensatory effort. The experiment did not directly measure that proposed mechanism, and the first experiment’s unsuccessful manipulation complicates any broad conclusion about beliefs.
Application to a DUI opinion
A claim such as “I can control myself after drinking” is different from a measured ability to cancel an action. These experiments give no basis for treating confidence as evidence of safe driving. They also do not prove that all observed impairment is an expectation effect.
No driving or collision task was performed. There was no sober baseline stop-signal measurement before the beverage, some task data were excluded or lost, and the study was powered around consumption rather than every cognitive interaction. Different taste-test beverages also limit comparisons between experiments.
Exposure was checked by breath testing rather than direct blood measurement. The authors acknowledged possible residual mouth alcohol, so the reported readings should not be treated as precise blood values or used to assign a personal impairment threshold.
The site’s comparison of voluntary stopping and stop-signal inhibition further explains why different forms of behavioral control should not be treated as interchangeable.
Primary source
Knibb G, Roberts CA, Robinson E, Rose A, Christiansen P. The effect of beliefs about alcohol’s acute effects on alcohol priming and alcohol-induced impairments of inhibitory control. PLOS ONE. 2018;13:e0201042. https://doi.org/10.1371/journal.pone.0201042.