Effects of clozapine, fluphenazine, and placebo on reaction time measures of attention and sensory dominance in schizophrenia.

Two reaction time (RT) paradigms were used to study clozapine's effects on sustained and selective attention compared to fluphenazine and placebo in 25 chronic schizophrenic patients. Sensory dominance was studied via simple and choice RTs to lights and tones, and on double-stimulus trials in which the two stimuli were presented simultaneously. Although 8 of the 25 patients could not perform the RT tasks when taking placebo, there were no effects of clozapine on simple or choice RT compared to placebo or fluphenazine. Subjects on all 3 treatments showed visual dominance: faster RT to lights than to tones on choice and double-stimulus trials. However, clozapine reduced this by means of a selective increase in RT to lights. Clozapine reduced failures to respond to the tone on double-stimulus trials. This was shown to be due to reductions in hallucinations. Clozapine does not generally improve attention, but it may increase the ability of schizophrenic persons to process nondominant or unattended stimuli possibly by increasing the efficiency of resource allocation. This may be partially mediated by a reduction in hallucinations.