Dissociating between sensory and perceptual deficits in PD: more than simply a motor deficit

Although Parkinson's disease (PD) is traditionally considered a motor output disorder, recent evidence suggests that people with PD may have sensory and perceptual impairments that may underlie movement impairments. Yet there has not been any direct testing of perceptual judgments, especially when manipulating the sensory feedback on which these judgments are made. The present study investigated how perception might be influenced by sensory feedback to contribute to height estimations and obstacle stepping in PD relative to healthy age-matched control participants. Perceptual judgment accuracy was evaluated by judging 3 typically encountered obstacle heights in 2 sensory feedback conditions: (1) vision of foot available and (2) without vision of foot (reliance on proprioceptive feedback to estimate height). Then participants proceeded to walk and step over the obstacle. Fifteen individuals with PD and 15 healthy control participants completed the task. As seen with toe elevation, toe elevation variability, and toe error measures, individuals with PD overestimated the obstacle height and were significantly more variable when relying solely on proprioception (in contrast to when vision was available) compared with healthy controls, although no differences between groups in obstacle crossing were found. These results support the notion that sensory deficits may contribute to inaccuracy of perceptual judgment and has the potential to contribute to gait behaviors such as tripping and falling, especially when vision is not available. Future studies should carefully consider the impact of sensory and perceptual deficits that might contribute to movement planning problems and consequentially movement impairments.