Effect of acute alcohol on attention and the processing of hierarchical patterns

Subjects received 100-msec exposures of hierarchical patterns consisting of a large "global" letter composed of several smaller "local" letters. Subjects were to respond whether a target letter was present at the global or at the local level. In the Neutral Bias condition target letters occurred randomly and equally often at the global and local levels. In the Global Bias condition, 79% of the targets occurred at the global and 21% at the local level. In the Local Bias condition, 79% of the targets occurred at the local and 21% at the global level. Subjects indicated by pressing a key which of two target letters had appeared on that trial. Subjects received either a placebo drink, a drink containing 0.7 ml of Alcohol per kg body weight, or a drink containing 1 ml of Alcohol per kg body weight. Placebo subjects were better at detecting letters at the global than at the local level in the Global Bias condition, better at local than global in the Local Bias condition, and about equally good at both levels in the Neutral Bias condition. Alcohol had no effect on detection of letters at the local level in any of the bias conditions but reduced detection of letters at the global level except when subjects were biased globally. The data suggest that alcohol does not affect attentional capacity. Instead, alcohol seems to affect either how attentional capacity is allocated or the global processing mechanism itself.