Age differences in symbol-digit substitution task performance.

A decline in performance on the Digit Symbol Substitution test related to aging is well documented. There is no agreement on the reason for the decline, however. In part, the lack of consensus with regard to changes on the test may be attributed to the limitations imposed by comparing groups on a single performance measure. In the present study, three forms of a Symbol-Digit Substitution task that varied in difficulty level were administered to 125 persons between the ages of 30 and 92. On all forms there was a clear performance decline associated with age. The differences observed among the age groups were interpreted as evidence for a change in a sensorimotor component and in two information-processing operations: Symbol encoding and visual search.