Converging evidence for domain-specific slowing from multiple nonlexical tasks and multiple analytic methods

Older and young adults were tested on eight nonlexical tasks that overlapped extensively in complexity: disjunctive choice reaction time, line-length discrimination, letter classification, shape classification, mental rotation, visual search, abstract matching, and mental paper-folding. Performance on the first seven tasks was associated with equivalently low error rates in both groups, making it possible to directly compare their response times (RTs) on these tasks. Consistent with domain-specific slowing, the relationship between the RTs of the older adults and the RTs of the young adults was well described by a task-independent mathematical (Brinley) function. Evidence from this analysis and from analyses based on task-specific information-processing models leads to similar conclusions and provides converging support for general cognitive slowing in the nonlexical domain.