Semantic and cross-case identity priming in patients with Parkinson's disease.

Semantic and cross-case identity priming were investigated in nondemented patients with Parkinson's disease (PD) and controls using the Lexical Decision Task. Three conditions were administered that consisted of the presentation of prime and target word pairs. In the semantic priming condition the word pairs were semantically related (e.g., table-CHAIR), in the cross-case identity priming condition the word pairs consisted of the same word (e.g., noise-NOISE), and in the unrelated condition the word pairs were not related semantically (e.g., guns-DEEP). A fourth condition was also administered that consisted of the presentation of a prime word and a pronounceable nonword target (e.g., starved-FORVE). Participants were asked to indicate whether the target was a real word or a nonword. The prime and target were separated by either a short or long (250 ms or 1000 ms) stimulus onset asynchrony (SOA). Results indicated that PD patients displayed normal semantic priming (i.e., faster responding to the target in the semantic condition as compared to the unrelated condition) at both the short and long SOA. Similarly, PD patients displayed normal cross-case identity priming (i.e., faster responding to the target in the identity condition relative to the unrelated condition) at the long SOA. At the short SOA, however, PD patients displayed hyper identity priming relative to controls (134 ms vs. 50 ms). These results suggest that semantic processes are normal in nondemented PD patients but that the processes involved in accessing lexical information may be overly activated in these patients.