Effects of lorazepam on the distribution of spatial attention.

Reaction time (RT) to stimulus events was assessed for 2 tasks with different spatial attention demands before and after receiving either a placebo or lorazepam (1 mg). In 1 task (onset), 12 participants responded to the onset of 1 of 5 potential dot targets contained within either a small or large area. In the other task (offset), all 5 targets were illuminated and 12 participants responded to the offset of 1 of them. In the onset task, lorazepam slowed RT equally for both the large and small display areas. In the offset task, substantial impairment was found with the large but not the small display area. Results are consistent with the hypothesis that lorazepam interferes with the processes involved in the movement of spatial attention. The possibility that lorazepam selectively impairs the disengage component of attentional movement is discussed.