Decreased semantic competitive inhibition in Parkinson's disease: Evidence from an investigation of word search performance

Aberrant semantic competitive inhibition has been reported in Parkinson's disease (PD). Whether PD-related alterations cause an increase or a decrease in lateral inhibition, however, remains unclear. Accordingly, the present study aimed to examine semantic inhibition during lexical-semantic processing in non-demented people with PD. Twenty-two people with PD and 18 matched controls completed a computerized word search task in which both the relationship between the background items and the target (related or unrelated) and the search type (open e.g., any dog or closed e.g., collie) were manipulated. It was hypothesized that decreased semantic inhibition would be evidenced by abnormally short response times for open searches among words related to the target, while increased inhibition would lead to abnormally long response times. Analysis of the results revealed that control participants performed open searches faster for unrelated vs related word lists. In contrast, the PD group recorded similar response times regardless of background items. Hence, the present findings are consistent with the notion of decreased semantic competitive inhibition in PD and suggest that an impaired ability to inhibit unwanted information during lexical retrieval may underlie observed deficits on semantic tasks such as verbal fluency.