A specific shifting deficit in Parkinson's disease: A reversal shift of consistent stimulus-response mappings

Two experiments were designed to investigate effects of cueing upon aptitud e for shifting by patients with Parkinson's disease. Subjects executed in a lternation two different components of a task set over successive items in a list. We compared the costs of shifting when the stimulus ensemble remain ed constant from trial to trial ("uniform" lists), with the case in which a change of stimulus ensemble cued each shift of task ("mixed" lists). Shift costs with mixed lists mere significantly smaller than those with uniform lists (Exp. 1, ns=12). This suggests that patients with Parkinson's disease can benefit from cues about the stimulus ensemble in performing tasks. Pat ients' shifting performance was different from that of controls only in a r eversal shift condition of the previously consistent stimulus-response mapp ings (Exp. 2, ns = 12). This result suggests that patients with Parkinson's disease suffer from a specific bur not a general deficit in ability to shi ft.