Sequential and coordinative complexity in time-accuracy functions for mental arithmetic.

Time-accuracy functions for tasks involving single-digit mental addition and subtraction were derived in a sample of 18 younger (mean age = 21.7 years) and 16 older adults (mean age = 68.8 years). Sequential complexity was manipulated by varying the number of operations (5 vs. 10); coordinative complexity was induced by bracketing. Age differences were apparent in the coordinative conditions, even though no age difference was present in the sequential conditions. This indicates that the age difference under conditions of high coordinative demands could not be attributed solely to a decline in basic speed of processing. The Age x Complexity interaction was due to larger onset times and lower asymptotic performance by the older adults in the coordinative conditions but not due to to rate of approach to the asymptote. This implies that coordinative demands do not differentially hurt access from semantic memory in older adults; however, coordinative demands do have disproportionately negative consequences for computation speed and self-monitoring in older adults.