Dissociating Between Sensory and Perceptual Deficits in PD: More Than Simply a Motor Deficit Kaylena A. Ehgoetz Martens, BSc and Quincy J. Almeida, PhD* Sun Life Financial Movement Disorders Research and Rehabilitation Centre, Wilfrid Laurier University, Waterloo, Ontario, Canada ABSTRACT: Although Parkinson’s disease (PD) is traditionally considered a motor output disorder, recent evidence suggests that people with PD may have sen- sory 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 feed- back to contribute to height estimations and obstacle stepping in PD relative to healthy age-matched control participants. Perceptual judgment accuracy was eval- uated 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 par- ticipants proceeded to walk and step over the obstacle. Fifteen individuals with PD and 15 healthy control par- ticipants completed the task. As seen with toe eleva- tion, 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 avail- able) compared with healthy controls, although no dif- ferences 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. V C 2011 Movement Disorder Society Key Words: Parkinson’s disease; basal ganglia; obstacle crossing; perception; proprioception Tripping over obstacles is a common cause of falls in Parkinson’s disease (PD), 1 yet why PD patients have greater difficulty stepping over obstacles is not well understood. Research suggests that hypokinesia com- promises the approach and crossing over of obstacles since individuals with PD have slower and smaller steps, resulting in a premature step over the obstacle. 2,3 Interestingly, sensory 4,5 and perceptual 6 deficits have recently been identified in PD and may have an impor- tant contribution to hypokinesia. For example, percep- tual speed deficits have been identified in PD during inspection time tasks (ie, tasks that require accurate identification of physical properties of a stimulus). 6 These sorts of perceptual deficits have been argued to contribute to movement since definitive changes in the spatiotemporal characteristics of gait can be identified well before a freezing of gait episode at a narrow doorway. 7 Hence, it is possible that impaired percep- tual processing might lead to judgment errors that could increase the likelihood of tripping over an obsta- cle. Therefore, if PD patients were impaired in their ability to accurately identify characteristics of the environment (such as obstacle height or door width), it might be difficult for them to plan a movement response appropriately. Alternatively, since humans rarely look at their feet just as they are stepping over obstacles, 8 it may be that a sensory deficit impairs awareness of foot loca- tion during clearance of an obstacle. Sensory deficits ------------------------------------------------------------ Additional Supporting Information may be found in the online version of this article. *Correspondence to: Quincy J. Almeida, Sun Life Financial Movement Disorders Research and Rehabilitation Centre, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario, Canada N2L 3C5; qalmeida@wlu.ca Funding agencies: This work was funded by the Natural Sciences and Engineering Research Council of Canada (to K.E.M. and Q.J.A.), the Canadian Foundation for Innovation (to Q.J A.), and the Canadian Institutes of Health Research. Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 20 May 2011; Revised: 18 October 2011; Accepted: 24 October 2011 Published online 15 December 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/mds.24042 RESEARCH ARTICLE Movement Disorders, Vol. 27, No. 3, 2012 387