Alcohol increases commission error rates for a continuous performance test

Studying the effects of alcohol on Continuous Performance Test (CPT) performance was of interest for two reasons, i.e., (1) perhaps because of the ease of the task used in previous experiments, alcohol has not been found to impair performance, and (2) CPT commission errors (described below) have been related to impulsive behavior.

In this study, the CPT featured both an Immediate Memory Task (IMT) and a more difficult Delayed Memory Task (DMT). We compared the performance of 18 subjects under both alcohol and placebo conditions, using a within-subject design. Both the IMT (0.5-sec delay) and the DMT (3.5-sec delay, with distracter stimuli at 0.5-sec intervals) required the subject to respond if a briefly displayed number was identical to the one presented before it. Stimuli included target (identical match), catch (4 of 5 digits matched), and novel (random number) stimuli. On 2 separate days, subjects performed between administrations of three hourly placebo drinks or three hourly drinks containing 0.20 g/kg of alcohol (producing peak breath alcohol concentrations of approximately 0.035%).

The main finding was that alcohol consumption increased responses to catch stimuli (i.e., commission errors) in the DMT. In contrast, performance in the IMT (the easier task) was unaffected by alcohol. Commission errors measured during peak breath alcohol concentrations were significantly correlated with scores on the Barratt Impulsivity Scale for both the IMT and DMT. Discriminability (A') between target and catch stimuli was reduced by alcohol for the DMT only.

These data indicate that even small amounts of alcohol can produce measurable changes in CPT performance parameters if the task is of sufficient difficulty and that commission errors can be increased by alcohol consumption.