Dual-task performance in demented and nondemented elderly

The present study examined the ability of demented and nondemented elderly subjects to divide their attention between recalling digits and judging the similarity of pairs of letters. Both groups showed substantial decrements in digit recall following distraction by letter matching. To identify the nature of the interference effect, digit recall was scored according to a strict criterion where preservation of the serial order of the digits was required (order-based recall), and a lenient criterion where preservation of digit order was not required (order-free recall). While both groups showed a comparable decrement in order-based recall due to the interfering task, order-free recall virtually eliminated the decrement for the nondemented group whereas substantial interference was still observed in the demented group. These results suggest that letter matching interferes with digit recall in nondemented elderly primarily by disrupting order information. In the case of demented elderly, letter matching disrupts the preservation of item information as well.