LORAZEPAM, A BENZODIAZEPINE, INDUCES ATYPICAL DISTRACTOR EFFECTS WITHCOMPOUND STIMULI - A ROLE FOR LINE-ENDS IN THE PROCESSING OF COMPOUNDLETTERS

The present study was designed to dissociate the effect of a single do se of lorazepam (a benzodiazepine, GABAA-agonist) on the processing of spatial frequency, visual integration, and attentional processes in h ealthy volunteers. The stimuli were composed of small letters spatiall y organized to form a large letter. The task was to decide which of tw o 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 target would appear at the local or at the global level. The results showed no evidence of a lorazepam effect on spatia l frequency or attentional processing, but there was an atypical distr acter effect when the target was a large letter, related to the arrang ement of line-ends. The results are discussed in relation to studies s howing the involvement of GABA in the generation of neuronal responses to line-ends.