EFFECTS OF LORAZEPAM ON PERCEPTUAL INTEGRATION OF VISUAL FORMS IN HEALTHY-VOLUNTEERS

We tested whether lorazepam (a benzodiazepine) affects perceptual proc esses involved in the computation of contour information. Subjects mat ched incomplete forms whose contour was composed of line segments vary ing in their spacing and in their alignment. An initial centrally disp layed object( a reference) was followed by two laterally displayed pic tures, a target and a distracter. The distracter was the mirror-revers ed version of the target. In one condition, the reference was always a n outline drawing of an object. In another condition, the reference wa s either an outline drawing or an incomplete form. All subjects were r un in both conditions. Lorazepam 0.038 mg/kg induced a larger increase in RTs than the placebo and lorazepam 0.026 mg/kg when the spacing be tween local contour elements was larger than 10.8' arc and when the li ne segments were not aligned. Performance was improved in the 0.038 mg /kg lorazepam group when subjects started with the condition in which the reference was always an outline drawing. Performance was not corre lated with sedation. These results show that lorazepam impairs visual perception. They are interpreted in terms of impaired binding processe s, which can be compensated for by the use of stored object representa tions. This effect is consistent with electrophysiological studies sho wing that the neuro-mediator GABA is involved in perceptual processes.