Lorazepam, a Benzodiazepine, Induces Atypical Distractor Effects with Compound Stimuli: A Role for Line-ends in the Processing of Compound Letters

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Abstract
The present study was designed to dissociate the effect of a single dose of lorazepam (a benzodiazepine, GABAA-agonist) on the processing of spatial frequency, visual integration, and attentional processes in healthy volunteers. The stimuli were composed of small letters spatially organized to form a large letter. The task was to decide which of two target letters was displayed, either as a small or the large letter. Effects of spatial frequency and attentional processing were explored by manipulating respectively the visual angle of the stimuli and the probability that the targetwould appear at the local or at the global level. The results showed no evidence of a lorazepam effect on spatial frequency or attentional processing, but there was an atypical distractor effect when the target was a large letter, related to the arrangement of line-ends. The results are discussed in relation to studies showing the involvement of GABA in the generation of neuronal responses to line-ends.