Sixteen male alcoholics were shown pairs of light flashes separated by intervals ranging from 0 to 100 msec., and judged whether there were one or two flashes. Two-flash fusion theshold (TFT) was raised by administration of promazine hydrochloride, a tranquilizing drug, and was higher for strict than for lenient instructions. Signal detection analysis showed that the drug reduced sensitivity but did not affect criterion, while instructions altered criterion placement without changing sensitivity.
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