Visual detection of affordances for aperture negotiation in people with Parkinson disease.

BACKGROUND: An essential requirement for the guidance of action in cluttered environments is that people can accurately perceive what actions are afforded by particular surroundings given the person's action capabilities. Research has shown that healthy young individuals turn their shoulders when walking through a doorway when the aperture is less than a certain percentage of their shoulder width and that they are able to detect this critical width with visual inspection. These findings imply that movements are constrained by perception of the environment in body-scaled unit. OBJECTIVES: The present work examined whether the visual affordance of doorway passability is altered in people with Parkinson disease (PD). METHODS: People with PD, healthy age-matched controls, and young adults (16 participants per group) walked through a series of apertures scaled to shoulder width. Participants also had to visually judge a series of apertures to determine if they could walk through the gap with their normal gait pattern. Finally, participants had to estimate their eye height. RESULTS: Statistical analysis revealed that people with PD initiated shoulder turning to go through the doorway at larger apertures (A) relative to their shoulder (S) width (A/S = 1.61) in comparison to healthy age-matched participants (A/S = 1.41) and young adults (A/S = 1.26). In comparison to healthy participants, People with PD also judged wider apertures as impassable. Individuals with PD were less accurate in their estimation of eye height (Error = 10.1%) than the healthy older (Error = 6.29%) and younger adults (Error = 4.79%). CONCLUSIONS: PD significantly impacted the affordances for aperture negotiation. Such altered perceptual affordances may contribute to gait pattern changes in people with PD when walking through doorways. These findings suggest that some of the motor symptoms in PD might have a perceptual underpinning.