Abstract
Purpose: :
Many real-world tasks consist of relative movement between observers and targets, evaluation of visual functions while targets and/or observers are in locomotion might better reflect individuals’ functional performances. In this study, we examined the impact of body motions on static and dynamic visual functions and their age-related changes.
Methods: :
Forty-three subjects with normal vision were recruited and divided into three age groups, 17 in young (18-30 years), 12 in middle-age (31-55 years) and 14 in elderly (>56 years). Visual acuity (VA) and contrast sensitivity (CS) were measured when stimuli moved at 4 speeds (0, 30, 60 and 90 deg/second) and observers posed sitting, stepping and walking on treadmill. Subjects were required to identify isolated letter (H, O, T or V) or grating orientations (vertical, horizontal, right or left) in VA and CS task respectively. Targets were shown by Psykinematix on a 50-in LCD monitor.
Results: :
Mixed between-within subjects ANOVA was used to study the impact of speeds, body postures and age on VA and CS. Increased stimuli’s speed significantly impeded VA and CS (p>0.10), reflecting little impact brought by locomotion. There was an aging effect on VA and CS (p<0.001). VA among three age groups was significantly different (p<0.001), but insignificant difference occurred between young and middle-age group in CS. Slope change in VA (-0.08 to -0.10) and CS (-0.14 to -0.20) among different speeds showed stronger age-related decline in CS. Interaction effect by body posture and age was insignificant in VA and CS; same result was also obtained when speed was considered. Significant interaction effect by speed and age was found in CS (p<0.001) but not in VA, indicating that moving speed affected older subjects’ CS more.
Conclusions: :
Visual functions were significantly influenced by moving stimuli but not by observers’ locomotion. Both VA and CS deteriorated when targets moved till 60 deg/second. Stronger age-related decline with the effect of speed suggested further study on the correlation of dynamic vision with functional performance in daily activity (e.g. balancing), which involves more low-contrast stimuli.
Keywords: aging: visual performance • aging