Alcohol and workload as factors affecting the detection of angular acceleration.
INTRODUCTION: Previous findings have demonstrated that a low blood alcohol concentration (BAC) decreases subjects' ability to detect changes in angular motion and that this effect persists after the BAC returns to zero. METHODS: Angular motion thresholds of six alcohol and six placebo subjects holding pilots' certificates were obtained under both low and high task load conditions. The alcohol subjects were tested under double blind conditions in an enclosed simulator apparatus prior to drinking, after drinking (mean BAC = 0.038%), and at a time when the alcohol subjects' BACs had reached zero. RESULTS: Alcohol subjects' mean threshold values for the three threshold test sessions were 0.361, 0.512, and 0.465 degree.s-2 and 0.292, 0.422, and 0.379 degree.s-2 for the high and low task conditions, respectively. Corresponding values for placebo subjects were 0.364, 0.37, and 0.356 degree.s-2 for the high task load condition and 0.311, 0.317, and 0.312 degree.s-2 for the low task load condition. Statistical analyses showed significant task load and sessions effects (p < 0.025). Significant alcohol by test sessions interactions were found for both high and low task load conditions (p < 0.01) with subsequent t-tests showing no alcohol-placebo differences for the pre-alcohol test session, but significant alcohol-placebo differences for the alcohol test session and the test session conducted after the subjects' BACs returned to zero. CONCLUSIONS: The results indicate that the increased threshold for detecting changes in angular motion found after alcohol ingestion is relatively insensitive to task workload and, thus, it is unlikely that attentional changes underlie the threshold increase. These data together with the finding that an elevated threshold can persist after BAC reaches zero suggest that the threshold increase after alcohol ingestion reflects changes in vestibular functioning.