Cognitive determinants of performance on the digit symbol-coding test, and the symbol search test of the WAIS-III, and the symbol digit modalities test: An analysis in a healthy sample

Whilst many investigators contend that the Digit Symbol-coding test (DSCT) is the test most sensitive to brain impairment within the Wechsler scales, little agreement has been achieved with regard to what the: test actually does measure. One hundred and two participants were administered a battery of 14 neuropsychological tests, which were grouped into domains of cognitive functioning. These were premorbid factors, reaction time, motor execution, incidental learning, visual-spatial memory, working memory, and executive functioning. Hierarchical regressions were performed an three criterion variables (DSCT, Symbol Digit Modalities Test, and the Symbol Search subtest), each of which has been previously reported to measure the concept of processing speed. The results indicated that only tests of motor execution contributed significantly to performance on all three criterion variables. These findings indicate that the ability to execute elementary motor operations is a significant factor in performance of these tasks, and that the complex construct of "processing speed" requires further delineation.