Older adults and stroke survivors are steadier when gazing down

Abstract

Background Advanced age and brain damage have been reported to increase the propensity to gaze down while walking, a behavior that is thought to enhance stability through anticipatory stepping control. Recently, downward gazing (DWG) has been shown to enhance postural steadiness in healthy adults, suggesting that it can also support stability through a feedback control mechanism. These results have been speculated to be the consequence of the altered visual flow when gazing down. The main objective of this cross-sectional, exploratory study was to investigate whether DWG also enhances postural control in older adults and stroke survivors, and whether such effect is altered with aging and brain damage. Methods Posturography of older adults and stroke survivors, performing a total of 500 trials, was tested under varying gaze conditions and compared with a cohort of healthy young adults (375 trials). To test the involvement of the visual system we performed spectral analysis and compared the changes in the relative power between gaze conditions. Results Reduction in postural sway was observed when participants gazed down 1 and 3 meters ahead whereas DWG towards the toes decreased steadiness. These effects were unmodulated by age but were modulated by stroke. The relative power in the spectral band associated with visual feedback was significantly reduced when visual input was unavailable (eyes-closed condition) but was unaffected by the different DWG conditions. Conclusions Like young adults, older adults and stroke survivors better control their postural sway when gazing down a few steps ahead, but extreme DWG can impair this ability, especially in people with stroke.

Gazing Down Has benefits Unrelated To Visual Input

“…Greater neck flexion might pose additional/different constraints that could be better handled using a hip strategy [35]— that is, hip flexion with a backward shift of the pelvis, resulting in a backward shift of the COP. In fact, in a previous report from our laboratory [21], we observed that extreme neck flexion decreased postural steadiness, an observation consistent with Buckley’s report. The ankle-vs.-hip strategy (actually, Horak and Nashner proposed that these two reside on the same continuum) may explain the difference in the direction of COP shift, but not the different effects on body sway.…”

“…Importantly, a significant ‘Vision’-by-’Angle’ interaction, which was required to support our main hypothesis, was not observed. The observed main effects of visual input and of stroke are consistent with current literature, including previous reports from our own laboratory [20,21] and will not be further discussed.…”

“…Recently, Koren et al [20] reported that DWG enhanced postural steadiness of standing and walking younger adults. These authors also found a similar effect with older adults and PwS [21], two populations that excessively rely on visual input and are more likely to gaze down while walking [22,23]. Based on previous literature, they further speculated that DWG enhances postural control primarily through its effect on the visual (retinal) input.…”

“…Given that we were (mostly) interested in the interaction term (‘Vision’ by ‘Angle’) and not the main effect of the angle, we decided to recruit 20 participants in each group. This value is much greater than that previously estimated [21], and is probably the result of testing participants in a wide-base-stance instead of narrow-base-stance, which is more sensitive to postural instability [30].…”

“…To estimate the number of participants required to show an effect of DWG on postural sway, we used the data collected from our previous study, which included four participants (one older adult and three PwS) who were tested in a wide-base stance [21]. We used the ‘SIMR’ package [28] in R (Version 4.0.5), in conjunction with the ‘lme4’ package [29].…”