Categorization system-switching deficits in typical aging and Parkinson's disease.

OBJECTIVE

Numerous studies documenting cognitive deficits in Parkinson's disease (PD) revealed impairment in a variety of tasks related to memory, learning, and attention. One ubiquitous task that has not received much attention, is categorization system-switching. Categorization system-switching is a form of task-switching requiring participants to switch between different categorization systems. In this article, we explore whether older adults and people with PD show deficits in categorization system-switching.

METHOD

Twenty older adults diagnosed with PD, 20 neurologically intact older adults, and 67 young adults participated in this study. Participants were first trained in rule-based (RB) and later information-integration (II) categorization separately. After training on the tasks, participants performed a block of trial-by-trial switching where the RB and II trials were randomly intermixed. Finally, the last block of trials also intermixed RB and II trials were randomly but additionally changed the location of the response buttons.

RESULTS

Contrary to our hypothesis, the results show no difference in accuracy between older adults and people with PD during the intermixed trial block, as well as no difference in response time (RT) switch cost. However, both groups were less accurate during intermixed trial blocks and had a higher RT switch cost when compared with young adults. In addition, the proportion of participants able to switch systems was smaller in people with PD than in young adults.

CONCLUSIONS

The results suggest that older adults and people with PD have impaired categorization system-switching ability, and that this ability may be related to a decrease in tonic dopamine (DA) levels associated with normal aging and PD. (PsycINFO Database Record