Effect of obstacle contrast on visual behaviour in Parkinson’s disease

L. Alcock; B. Galna; J. Hausdorff; L. Rochester

[Poster] BACKGROUND AND AIM: The ability to safely negotiate obstacles is important for independent mobility. Appropriate processing of visual information helps to identify and distinguish environmental obstacles and their location. Visual function is compromised in people with Parkinson’s disease (PD) with respect to appropriate observation of the environment and is linked to poorer attention[1] and impaired contrast sensitivity[2]. Together they may contribute to falls in PD during challenging tasks such as obstacle crossing[3]. The aim of this study was to determine the effect of obstacle contrast on visual behaviour and whether this was altered in PD. METHODS: Seventeen mild-to-moderate PD fallers (x̅[SD]age:71.1[8.2]y, 10♂) and 18 older adult non-fallers(x̅[SD]age:64.4[7.0]y, 9♂) participated. Participants began the walking trials with their eyes closed and when prompted opened their eyes and walked to the end of a 10-metre walkway. An obstacle of high or low contrast (HxWxD 15cmx60cmx2cm) was placed half way down the walkway and the presentation order was counterbalanced. Visual behaviour was monitored using a mobile eye-tracker (Dikablis) and contextual outcomes were extracted from the approach phase (Approach time[s], movement latency[s], time spent looking at the obstacle[%], time spent looking at the ground preceding the obstacle[%] and time spent looking at the ground past the obstacle[%]). Contrast sensitivity was measured binocularly (Mars CS chart). Group medians were used to complete non-parametric comparisons between groups and obstacle conditions. RESULTS: Contrast sensitivity was significantly reduced in PD (x̅[SD]:1.51[0.16] vs. 1.64[0.07],p=.006). There were no group differences in visual behaviour when negotiating the high contrast obstacle (p=.126), movement latency (p=.858) and the time spent looking at the ground past the obstacle (p=.143). There was a trend for PD to spend longer looking at the obstacle but this was not significant (p=.067). In the low contrast obstacle condition, PD took significantly longer during their approach to the obstacle (4.2s vs. 3.1s, p<.001) and spent longer looking at the obstacle as a proportion of the approach phase (51.5% vs. 22.7%, p=.025) compared to the older adults who spent proportionally more time looking at the ground beyond the obstacle (75.0% vs. 29%,p=.007). CONCLUSIONS: The clarity of obstacles influences visual behaviour. Our findings suggest that increased contrast improves visual behaviour in PD so that it becomes similar to older adults. When obstacle contrast was low, participants with PD prolonged their visual attention to the obstacle to gather sufficient information regarding the obstacle proximity and dimensions limiting their capacity to scan for future obstacles. Future studies will explore the manipulation of contrast within natural environments where the presence and location of trip hazards such as obstacles are not known. REFERENCES: [1]Galna 2012 BrainRes 1473 35-43 [2]Hwang 2013 J Neurosci 33 14989-14997 [3]Gazibara 2014 Geriatric Nursing 35 364-369

Effect of obstacle contrast on visual behaviour in Parkinson’s disease

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