LORAZEPAM IMPAIRS PERCEPTUAL INTEGRATION OF VISUAL FORMS - A CENTRAL EFFECT

Previous studies have shown a lorazepam effect on visual perception. W e tested whether this impairment resulted from a peripheral effect ind uced by benzodiazepines. A first experiment showed that a single dose of lorazepam induces an oculomotor imbalance without impairing visual acuity or accommodation. In a second experiment, we tested whether the impairment induced by lorazepam on visual perception still occurred i n monocular vision. Subjects matched incomplete forms controlled on th e spacing and alignment of their local contour elements. A reference o bject was first displayed and followed by two laterally displayed obje cts, a target and a distracter. The distracter was the mirror-reversed version of the target. Performance was impaired in the lorazepam grou p when the reference was an incomplete form with a spacing of 10.8' or 22.2' of are. These results were not correlated with sedation. They c onfirm that lorazepam has a central deleterious effect on visual perce ption. A post-hoc analysis also suggested that lorazepam-treated subje cts used asymmetry in the stimuli as a compensatory strategy. This res ult is discussed in relation to previous hypotheses about the physiolo gical mechanisms that determine the effects of lorazepam on visual per ception.