Abstract

This study investigated the relationship between cognitive inhibition and set-switching costs in 13 patients with Parkinson's disease (PD) and 16 control subjects using a set-switching task with fully predictable switches. Incongruent colour-words and numerals were presented in either baseline (only colour-words or only numerals) or alternating lists (colour-words and numerals in alternation). Words required either a word-reading or colour-naming response whereas numerals required either a value-naming (value of the digits) or group-size naming (number of digits) response. Stroop interference was found to be increased and practice effects on nondominant tasks reduced in PD patients, suggesting that the ability to increase control over interference from irrelevant prepotent responses may be implicated in PD. Switch costs of PD patients were reduced on the first few trials of alternating dominant task lists and increased towards the end of alternating nondominant task lists. Both effects were explained as resulting from a reduced ability to maintain task-sets where selection of correct responses relies on inhibition of irrelevant stimulus-response mappings.