Subject performed a divided attention task in which they detected occurrences of a target letter in a stimulus figure which was a large letter made up of an array of small letters. Subjects pressed one button if the large letter was the target, another if the small letters were the target.
Performance on this task was compared to other attention and psychomotor tasks in a three-way randomized crossover study comparing two doses of alcohol with placebo in 12 healthy volunteers (six male, six female, aged 19-41). The higher dose of alcohol produced blood concentrations of 43 mg/100 ml, the lower dose 16 mg/l00 mi.
Subjects reported themselves significantly more drunk on both doses of alcohol than on placebo, showed poorer long-term recall on the Buschke selective reminding task than on placebo, and made more errors on a letter cancellation task. They performed letter cancellation faster, however. No significant effects were seen on the divided attention or continuous attention tasks, though continuous attention showed a trend towards impairment.
These results suggest that the greater sensitivity showed by some multiple task combinations to low doses of drugs such as alcohol is not due to divided attention as such, but results from some aspect of task combination. The coupling of increased errors but increased speed on letter cancellation has obvious implications for the interpretation of the effects of alcohol on complex real-life tasks such as driving.