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

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. 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. 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. 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. 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.