Empirical separation of physiologic and expected effects of alcohol on complex perceptual motor performance.

The role of expectancy in producing perceptual motor-performance deficits following alcohol consumption was investigated in a 2 X 2 factorial experiment. Forty male normal drinkers (1) either were or were not administered 0.414 g ethanol/kg body weight and (2) either were or were not instructed they were consuming an alcoholic beverage (regardless of actual beverage content). Performance on a divided-attention task requiring simultaneous pursuit rotor tracking and choice reaction-time responding provided the main dependent measures. Alcohol disrupted tracking performance and interacted with instructions regarding beverage content to influence choice reaction-time performance. Results confirmed previous reports of divided-attention task performance deficits induced by a low alcohol dose, but, more importantly, indicated that subjects' expectancies also influence performance levels. These findings demonstrate the importance of controlling for expectancy effects in alcohol research, and suggest that alcohol and expectancy may influence perceptual motor performance through different processes.