Social drinkers underestimate the additive impairing effects of alcohol and visual degradation on behavioral functioning

Rationale: Studies have shown that social drinkers are poor estimators of alcohol-induced impairment. Underestimates of blood alcohol concentration and other indices of intoxication are associated with decisions to perform risky behaviors, such as operating a motor vehicle. It is possible that self-evaluations of impaired functioning under alcohol might be particularly compromised in the presence of other sources of impairment. A common source of impairment that co-occurs with alcohol is visual degradation. Objectives: The present study compared actual and self-evaluated impairment in response to four conditions (0.65 g/kg alcohol, degradation of task-relevant stimuli, alcohol plus visual degradation, and no-treatment control) to determine whether social drinkers would perceive an increase in impairment from the combined treatments. Methods: Actual psychomotor impairment was measured in 16 social drinkers (eight men) by a pursuit rotor task and their self-evaluations of this impairment were obtained on a rating scale. Results: Alcohol and visual degradation impaired participants' actual performance to a similar degree and, in combination, the impairing effects were additive. Participants' self-evaluation ratings showed that they underestimated the additive impairment produced by the combination of alcohol and visual degradation. Conclusions: The findings suggest that social drinkers might be unable to appreciate an increase in behavioral impairment when alcohol is consumed in the context of another impairing influence.