1. Figure 2. Change in saccade frequency (without vs with a visual cue)
People with Parkinson’s disease increase visual sampling during gait in response to visual cues Stuart S, Galna B, Lord S, and Rochester L Institute for Ageing and Health, Newcastle University
Methods
Introduction
Visual sampling was measured in 7 subjects with PD and 7 healthy older adults (>50 years) (controls). The data was collected using an infra-red mobile eye-tracker (50Hz) (Dikablis), which was synchronised with a 3D motion capture system (Vicon).
Participants walked straight under 4 conditions; with and without a door and with and without a visual cue (transverse tape lines).
The primary outcome measure for this study was visual sampling; specifically saccadic frequency (number of saccades per second) during gait. A saccade (fast eye movement) was classed as an eye movement with a velocity threshold of ≥240 degrees/second (~5° amplitude).
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 remains unknown, although intact attention is likely to be required.
This study describes preliminary work assessing visual sampling in PD during walking under different conditions (i.e. without and with visual cues), and reports preliminary, descriptive results.
Trial duration (%)
Start
Door 0%
100%
Left and Up Saccade
Up Saccade
Horizontal
Vertical
Results
Figure 2 Layout of walking conditions
Figure 3 Eye-tracker positioning
Figure 1 Example of eye tracker data trace
PD (n=7) and control (n=7) participants had normal cognition (MoCA >26). PD participants had poorer scores for attention, executive function and visual functions, which are commonly impaired in PD [2].
Saccade frequency
Control participants made more frequent saccades during walking without a visual cue than PD participants (Figure 1), but did not change their saccadic frequency with a visual cue.
PD participants increased their saccadic frequency in response to a visual cue (Figure 2).
Table 1.
Demographic, clinical, cognitive and visual characteristics of PD and control participants.
Characteristic
PD (n=7) Mean (SD)
Control (n=7) Mean (SD)
Demographic
Age (years)
67 (5.6)
55.6 (3.5)
Sex
6 m, 1 f
3 m, 4 f
Clinical
Hoehn & Yahr stage
2 (0.8) -
UPDRS Part III
29.7 (12.6)
Disease duration (years)
3.5 (3.5)
Freezing of gait questionaire
1.3 (3.9)
Geriatric Depression Scale
2.7 (3)
0.7 (.9)
Falls efficacy scale
22.6 (5.9)
17.3 (1.5)
Cognitive
Montreal Cognitive Assessment
27 (1.6)
28.6 (.5)
Addenbrookes cognitive examination
90.4 (5.4)
93.9 (3.6)
CDR: Power of attention
(277.8)
(71.2)
Judgement of line orientation
23.5 (4.95)
24 (4.3)
Royals CLOX 1
12.2 (1.23)
13 (1.1)
Royals CLOX 2
13.2 (1.23)
13.4 (1.1)
VOSP - Incomplete letters
19.6 (0.7)
19.3 (.5)
VOSP - Dot counting
9.90 (0.32)
10 (0)
VOSP - Position discrimination
17.4 (5.91)
19.3 (1.03)
Vision
Visual acuity (logMAR)
0.00 (0.08)
-0.1 (.11)
Contrast sensitivity (logCS)
1.59 (0.10)
1.65 (0.07)
Figure 2. Change in saccade frequency (without vs with a visual cue)
Conclusions
In contrast to healthy controls, people with PD respond positively to visual cues.
Response to visual cues is evidenced by increasing saccadic frequency - possibly mediated by attention.
In non-cued conditions people with PD present make fewer saccades compared with controls.
Further work on a larger sample (n = 40 controls, 60 PD) will provide more definitive results.
References
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)
Stuart, S., et al., The measurement of visual sampling during real-world activity in Parkinson's disease and healthy controls: A structured literature review. J Neurosci Methods, : p
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."