Effects of moderate dose alcohol on visual contrast sensitivity for stationary and moving targets

Contrast sensitivity involves distinguishing threshold luminance differences and is usually assessed using static sine-wave gratings over a range of different spatial frequencies. The purpose of this study was to determine the effects of various levels of acute alcohol intoxication on contrast sensitivity to stationary and moving sine-wave gratings. Moving gratings required the subjects to make pursuit eye movements. A secondary goal was to investigate whether any alcohol-related effects were associated with any measures of intoxication.

Male volunteers (N = 8) participated in three counterbalanced, double-blind, testing sessions (low alcohol, moderate alcohol and placebo) plus a control session with no beverage. Breath alcohol concentration and two subjective measures of intoxication were measured for each subject. Static and dynamic contrast sensitivity were determined for electronically generated sine-wave gratings that were either stationary or traveled in a circular path with a diameter of 9 cm (3.7 degrees) at 51.7 rpm, thus requiring the subject to make smooth pursuit eye movements.

The mean blood alcohol concentration measured in the moderate alcohol condition was 0.043% and in the low alcohol condition 0.011%. Moderate dose alcohol consumption significantly impaired both static and dynamic contrast with a greater effect for moving targets.

Objective and subjective measures of intoxication were unrelated to the alcohol-related losses in contrast sensitivity. Although most states currently prohibit driving with BACs of 0.08-0.10%, the present data indicate reliable visual impairment at approximately half of that level (.44%).