Effective spatial orientation and postural control requires the integration of proprioceptive, vestibular and visual inputs. Increased visual dependence has been reported in older adults but the underlying mechanisms remain unknown. The aims of this research were to investigate the methodological issues relevant to assessment of visual dependence in healthy younger (18-40 yrs) and older (>60 yrs) subjects and also the effect of sensory manipulation (vibratory and auditory) on visual dependence and postural control. Visual dependence is commonly assessed by the Rod and Disc Test (RDT) and used throughout the thesis. Postural control was assessed by postural sway when standing on a force plate during static (one and two legged stance) and dynamic (stepping) tasks with eyes open (viewing static and rotating images) and closed. It was found in Chapter 2 that presentation shape (rectangular or round) had no effect on visual dependence. However pixellation on a TV screen could provide orientation cues to judge visual vertical i.e. decreased visual dependence as judged by the RDT and thus underestimates the amount of visual dependence. This was similar in both age groups. Visual stimulation can impair balance and there are reports of habituation in response to repetitive stimulation and also that the habituation is less in healthy older people. Little is known about the effects of repeated visual stimulation on visual dependence. There was no effect on visual dependence of repeated visual stimulation by the RDT with two recovery intervals (~7 and 10min) in either age group (Chapter 3). These findings suggest that visual dependence is less sensitive to visual stimulation than balance control. Whole body vibration (WBV) is a sensory stimulus that can improve muscle power and balance after a single session but its effects on sensory systems is less understood. Five minutes of WBV improved visual dependence in the younger group for 20 minutes (p=0.03 – 0.05) but had no effect in the older one (Chapter 4). No such compensation occurred in older people who may have a less flexible and slower sensory reweighting ability. In Chapter 5 balance control was assessed during standing on one and two legs when looking at both a static and rotating image also with eyes closed. There was a non-significant trend for balance improvement in both age groups. The sensory stimulation provided by WBV through proprioceptive and vestibular inputs may reduce reliance on vision. Divided attention may increase visual dependence and disturb balance, particularly dynamic balance. . Auditory distraction, in the form of recordings of real street sounds, did not change the level of visual dependence or balance control during static bipedal stance or dynamic (stepping) in either age group. However, it did increase postural sway during the more challenging task of standing on one leg in younger subjects (p=0.048) and showed a non-significant trend (p=0.07) to do so in the older subjects (Chapter 6). This was the only study to find higher levels of visual dependence in the older age group (p=0.02 – 0.0001). A key finding of majority of studies was the relatively similar level of visual dependence and response to sensory manipulation in the two age groups compared with the published literature, although the subjects studied were often older. They subjects were healthy and very active both physically and mentally and so may not be representative of their age group. This suggests that ageing per se may not necessarily lead to increased visual dependence in healthy people but relates to the development of specific pathologies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:628482 |
| Date | January 2014 |
| Creators | Lee, Shu-Chun |
| Publisher | King's College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://kclpure.kcl.ac.uk/portal/en/theses/effect-of-age-on-visual-dependence-for-spatial-orientation-and-postural-control(c1b24d43-43ba-47f9-803d-183fab3997e6).html |
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