Abstract
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.
Highlights
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
Aberrant controlled semantic activation was observed in the PD group on levodopa; automatic semantic activation was still evident
Semantic priming refers to the faster recognition of target words that are preceded by a related prime word compared to an unrelated prime word
Summary
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 [5,6,7,8] Despite these findings, the impact of PD on automatic versus controlled mechanisms of semantic processing is still unclear. 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) These semantic priming effects can be attributed to either automatic or controlled mechanisms. There are a number of critical variables that can be manipulated within an experiment in order to dissociate between these 3 mechanisms of priming [9], namely, the stimulus onset asynchrony (SOA) between prime and target, the proportion
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