Visual sampling during walking in Parkinson’s disease: impact of visual cues and task complexity Stuart S, Galna B, Lord S, and Rochester L Institute for Ageing and Health, Newcastle University
Introduction
Methods
Gait impairments are intrinsic to Parkinson’s disease (PD) and driven at least in part by visual and cognitive deficits [1]. Therapeutic interventions such as visual cues (e.g. coloured transverse tape lines) are used to alleviate walking disturbances associated with PD. However, the mechanisms by which cues work (and who they are best suited to) are unknown, although intact attention is likely to be required.
Visual sampling was measured in 3 subjects with PD and 3 healthy older adults (≥50 years old) (controls). The data was collected using an infra-red mobile eye-tracker (50Hz) (Dikablis), which was synchronised with a 3D motion capture system (Vicon).
This study describes the method used to examine visual sampling (i.e. the combination of fixations and saccades) in PD during walking under different conditions, and reports preliminary, descriptive results.
The primary outcome measure for this study was the number of saccades. A saccade (fast eye movement) was classed as an eye movement with a velocity threshold of ≥240 degrees/second (~5° amplitude).
Left and Up Saccade
Straight walk
Participants walked straight under 6 conditions; single and dual task, with and without a door and with and without a visual cue (transverse tape lines).
Straight walk through a door
Straight40° turn walk
40° turn starting Straight walk 10° off centre through a door
40° turn
40° turn starting 10° off centre
Up Saccade Horizontal
Vertical
2.5m
2.5m
0%
Trial duration (%)
100% Door
Start
0.8m
0.8m
Results
Figure 1 Example of eye tracker data trace
Figure 2 Layout of walking conditions
Figure 3 Eye-tracker positioning
The 6 participants all presented with normal cognition (Montreal cognitive assessment ≥26) Number of Saccades • The number of saccades increased with a visual cue • The visual cue increased the number of saccades during environment change (door) and dual tasking
Fixation Duration • Fixation duration decreased with a visual cue • The visual cue decreased fixation duration during environment change and dual tasking
Figure 4 Change in the number of saccades with vs without a cue
Figure 5 Change in fixation duration (seconds) with vs without a cue
Summary
References
Visual sampling increased with the use of a visual cue (transverse tape lines on the floor) in healthy controls and PD subjects, possibly due to heightened attention on the cue. The increase in saccade number coincided with reduced fixation durations. These preliminary results give an initial indication as to the mechanisms behind visual cues. Further work on a larger sample (n = 30 controls, n= 40 PD) is underway which will provide more definitive results.
1. Galna S, Lord S, Daud D, Archibald N, Burn D and Rochester L. Visual sampling during walking in people with Parkinson’s disease and the influence of environment and dual-task. Brain Research. 1473(2012) 35-43.
Acknowledgements This is a summary of independent research funded by the National Institute for Health Research (NIHR)'s Doctoral Fellowship Programme, the Newcastle Biomedical Research Unit based at Newcastle Hospitals NHS Foundation Trust and Newcastle University. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health."
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