Objective: The effect of alcohol on driving-related tracking tasks at four times of day was examined to address concerns that the legal driving alcohol threshold in New Zealand (80 mg/dl blood) may have greater effects during the early afternoon and early morning than during the evening and midmorning. Method: A volunteer group of 16 male army personnel provided a homogenous sample with respect to time-of-day characteristics. After a formal practice session, members of the sample performed lateral (one-dimensional) tracking tasks in eight counterbalanced sessions, either with or without alcohol (0.836 g/kg), at 0900, 1300, 1800 and 0100 hours. The tasks varied in terms of smooth and ballistic motor pursuit, unpredictability and availability of target preview. Results: Alcohol markedly impaired tracking accuracy (error from target), especially in nonpreview conditions. The only evidence for an overall time-of-day effect was on a ballistic pursuit nonpreview task, but there was no indication of any alcohol by time-of-day interactions. Conclusions: When tested 30 minutes after consumption of alcohol, sensorimotor tracking skills are markedly impaired at alcohol levels approaching the New Zealand threshold for legal driving, but these effects are not subject to circadian variations.
