Two semantic priming tasks, designed to isolate automatic and controlled semantic activation, were utilized to investigate the impact of dopamine depletion on semantic processing in Parkinson's disease (PD). Seven people with PD (tested whilst on and off levodopa medication) and seven healthy adults participated in the study. The healthy adult participants demonstrated intact automatic and controlled semantic activation. Aberrant controlled semantic activation was observed in the PD group on levodopa; however, automatic semantic activation was still evident. In contrast, automatic semantic activation was not evident in the PD group off levodopa. These results further clarify the impact of PD on semantic processing, demonstrating that dopamine depletion can cause disturbances in both automatic and controlled semantic activation. 1. Introduction Studies of language processing in Parkinson’s disease (PD) have provided clear evidence that even in the absence of overt dementia, semantic processing impairments may be evident in some people with the disease. In addition to widely reported impairments to verbal fluency in PD [1], impairments have been observed on tasks involving action naming [2], the judgment of semantic attributes and hierarchies [3], semantic word search [4], and semantic priming [5–8]. Despite these findings, the impact of PD on automatic versus controlled mechanisms of semantic processing is still unclear. The present study sought to utilize measures of automatic and controlled semantic priming to further elucidate the impact of dopamine depletion on these mechanisms of semantic processing in PD. Semantic priming refers to the faster recognition of target words that are preceded by a related prime word (e.g., apple fruit) compared to an unrelated prime word (e.g., paper fruit). Importantly, these semantic priming effects can be attributed to either automatic or controlled mechanisms. Automatic semantic priming is fast acting and refers to the automatic spreading of activation from prime to target that occurs within semantic networks [9]. Controlled priming, on the other hand, is slower acting and is typically attributed to either prelexical expectancy generation or postlexical semantic checking strategies [9]. During prelexical expectancy generation, participants use the prime word to generate an expectancy set of possible target words that are related to the prime word. Lexical decisions are subsequently faster to related target words that were included within the expectancy set. In contrast, postlexical semantic matching involves
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