Predictive language comprehension in Parkinson’s disease

Language impairment in Parkinson’s disease (PD) may be attributable to motor and action/event knowledge deficits. We predicted that cognitively intact PD participants would be impaired in anticipating objects in sentences from event-based thematic fit information. Twenty-four PD and 24 healthy age-matched participants completed comprehensive neuropsychological assessments. We recorded participants’ eye movements as they heard predictive (The fisherman rocks the boat) and non-predictive baseline sentences (Look at the bathtub). Predictive sentences contained target, agent-related, verb-related, and unrelated images. Baseline sentences used phonologically and semantically unrelated distractors. We tested effects of group (PD/control) on gaze using growth curve models. There were no significant differences between PD and control participants in either sentence type, suggesting that PD participants successfully and rapidly use combinatory thematic fit information to predict upcoming language. Additionally, we conducted an exploratory analysis contrasting PD and controls’ performance on low motion content versus high motion content verbs. This analysis revealed fewer predictive fixations in high-motion sentences only for healthy older adults, suggesting that people with Parkinson’s disease may adapt to their disease by relying on spared, non-action-simulation-based language prediction and processing mechanisms. Given that multiple studies have shown that individuals with PD have difficulty processing verbs, it is highly surprising that they match healthy adults in their ability to use verb meaning to predict upcoming nouns.