The effect of alcohol on the vestibulo-ocular reflex and apparent concomitant motion.

Measures of the vestibulo-ocular reflex (VOR) and apparent concomitant motion (ACM), the apparent motion of stationary visual stimuli during head motion, were obtained during sessions in which subjects consumed either alcoholic or placebo beverages. Both VOR and ACM remained constant throughout the placebo sessions. During sessions in which alcohol was consumed, the gain of the VOR was reduced and there was an increased tendency to see ACM in the direction opposite head motion. The effects of alcohol on ACM were greatest 50 min following cessation of drinking, near the maximum of the blood alcohol concentration (BAC). ACM measures then returned towards baseline, whereas the BAC measures remained elevated. VOR gain alterations paralleled the BAC measures. Therefore, reduction of VOR gain with alcohol produces an increase of ACM, but the ACM changes are relatively transient when compared with the altered VOR gain.