The spatial magnitude of standing body sway is greater during viewing of more distant targets and reduced when viewing nearby targets. Classical interpretations of this effect are based on the projective geometry of changes in visual stimulation that are brought about by body sway. Such explanations do not motivate predictions about the temporal dynamics of body sway. We asked whether the distance of visible targets would affect both the spatial magnitude and the multifractality of standing body sway. It has been suggested that the multifractality of movement may change with age. Separately, previous research has not addressed the effects of target distance on postural sway in older adults. For these reasons, we crossed our variation in target distance with variation in age. In an open-air setting, we measured standing body sway in younger and older adults while looking at visual targets that were placed at three distances. The distance of visual targets affected the spatial magnitude of body sway in younger adults, replicating past studies. Target distance also affected the spatial magnitude of sway in older adults, confirming that this relation persists despite other age-related changes. Target distance also affected the multifractality of body sway, but this effect was modulated by age. Finally, the width of the multifractal spectrum was greater for older adults than for younger adults, revealing that healthy aging can affect the multifractality of movement. These findings reveal similarities and differences between the spatial magnitude and the multifractality of human movement.
Studies of Antarctic fauna have led to tentative identification of a range of potential pathogens for both animals and humans. The rapid increase in visitors on tourist ships to the continent, now exceeding 10,000 per year, raises the concern that humans might transmit pathogens into and between wildlife colonies. The authors investigated the feasibility and efficacy of chemical disinfection of the microbial contamination on visitors' boots. During three voyages to penguin colonies in the Ross Sea, swabs were collected from the boots of visitors prior to landing, immediately on return to the ship, after a water wash, and after a chemical disinfectant wash using Virkon S. For the first two visits, abundant growth of bacteria was identified on boots at all three stages prior to disinfection. Following disinfection, the growth of bacteria was virtually eliminated. On the third visit, previously disinfected boots grew virtually no bacteria. After this landing the bacterial growth was substantially reduced by disinfection. These results indicate that consideration should be given to including disinfection in cleaning the boots of visitors to wildlife sites in the Antarctic to reduce the risk of translocation of microbial pathogens.
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