Effects of psychotropic drugs on digit substitution: comparison of the computerized symbol-digit substitution and traditional digit-symbol substitution tests

The digit-symbol substitution test (DSST), performed with paper and pencil or computerized, is widely used to reveal decrements in human attention and cognition. We programmed sets of adjustable tasks (digit-symbol, digit-digit, symbol-digit, symbol-symbol) into a microcomputer and compared the symbol-digit substitution (SDST) and the digit copying test (DDCT) with the traditional DSST in two placebo-controlled double-blind studies of psychotropic drugs with pre-trained young healthy subjects. Performances were measured before drug intake and several times after it; matched, different codes were used at consecutive tests. DSST and SDST substitutions remained at the baseline level after placebo, while the simple DDCT performance improved during the placebo session. The prolonged (3 min) test was not exhaustive because interim counts at 90 s predicted the final performance well. In Trial I, 15 mg diazepam orally reduced DSST and SDST functions in a similar way, but it also impaired simple copying in the DDC...