Memory and motor skill components of the WAIS-III Digit Symbol-Coding subtest

We examined motor skill and memory components of the Digit Symbol-Coding subtest of the WAIS-III in a clinical sample. Research using previous versions of the WAIS in non-clinical samples has suggested that the age-related decline in Digit Symbol-Coding scores is more related to motor ability rather than to the memory requirements of the test. Our results extend this conclusion to a clinical sample, using the WAIS-II. Copy scores measure motor skill on the Digit Symbol-Coding subtest, and Incidental Learning scores (Free Recall and Pairing) measure memory. A large proportion of Digit Symbol-Coding variance was explained by Copy scores with Incidental Learning scores controlled, but Incidental Learning scores explained little additional variance when Copy scores were controlled. The same pattern was found when we used the Immediate Memory and General Memory Indexes from the Wechsler Memory Scale-II as independent measures of memory.