Ethanol and event-related potentials: the influence of distractor stimuli.

A modified auditory "oddball" task was employed to determine the effects of ethanol on event-related potentials (ERPs). Ten subjects ingested either a 0.0 or 1.0 ml/kg dosage of 94% ethanol on counterbalanced days. During each set of pre- and post-drug days, the subjects heard a frequently occurring 1000 Hz standard presented to the left ear, an infrequently occurring 2000 Hz target presented to the left ear, and an infrequently occurring 2000 Hz distractor presented to the right ear. The intensity of the distractor was varied in different conditions. Ethanol ingestion had a significant effect on a number of ERP components. The amplitudes of a vertex N1b and P2 were significantly attenuated suggesting that ethanol's influence on N1b is probably due more to a depressive effect operating at the level of sensation than on a decrease in the subject's state of attentiveness. P3 was found to be reduced in amplitude but only following the distractor and not the target, possibly reflecting an interaction of task difficulty or informational value of the stimulus. There was little evidence of a greater susceptibility of the right hemisphere compared to the left or of association areas compared to the auditory cortex.