Action and Event-Based Lexical-Semantic Processing in Parkinson's Disease.

We tested the hypothesis that Parkinson's disease (PD) impairs verbs' event structures and/or sensory-motor semantic features, as suggested by theories of grounded cognition. Nineteen participants with PD and 16 age-matched Controls produced verbs and used a Likert scale to rate verbs' event-based association with instruments (e.g., fork- eating versus bathing) and locations (e.g., airport- waiting versus singing). When producing instrument-related verbs, PD participants responded slower and had a lower proportion of relevant responses than Controls. Yet PD participants showed a relatively intact ability to produce location-related verbs and to rate instrument- and location-related verbs. Greater motor disease primarily impacted instrument-related verb production. 4/19 PD participants had mild cognitive impairment (per Movement Disorders Society criteria), which affected both instrument- and location-related verb production and ratings. Overall, results were consistent with 'weak' grounded cognition theories that propose that sensory-motor simulation may enrich action-semantic processing but is not strictly necessary for action-semantic processing.