Impaired set-shifting in Parkinson's disease: new evidence from a lexical decision task

On a lexical decision (LD) task, participants quickly decide whether a target letter string is a word. When a target word (e.g., CARROT) is preceded by a category cue (e.g., VEGETABLE), participants respond more quickly than when the target is preceded by a semantically neutral cue (e.g., BLANK). Previously, Spicer, Brown, and Gorell (1994) reported that patients with PD, when tested with a variation of Neely's (1977) LD task, showed hyperpriming. That is, patients with PD exhibited a larger difference in reaction time between the neutral cue and category prime conditions than did controls. The present study found little evidence that PD hyperpriming was explained by difficulties accessing semantic information. Rather, hyperpriming appeared to be related to a general tendency among a subgroup of patients with PD to perseverate.