Development and Maturation of Global Motion Sensitivity in Children of Kathmandu
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Introduction: Global motion processing is an essential part of visual perception involving higher cortical areas. The motion coherence threshold (MCT) is used to evaluate global motion processing. Previous studies have investigated the development of translational optic flow processing in children but no study has yet evaluated MCT for radial optic flow. Previous studies have proposed different channels for processing slow and fast motion. The aim of this study was to investigate the development and maturation of optic flow processing in children and to explore the effect of speed and different types of optic flow stimuli. Methods: A total of 125 children, aged from 6 to 16 years and 24 adults, with normal ocular health, participated. The children and adults were evaluated with optic flow patterns at a relatively fast (5.48°/s) and a relatively slow (1.56°/s) speed at a Michelson contrast level of 75%. A pilot study involving four observers was carried out to establish the optimum values for speed and contrast to be used in the main study. A random dot kinematogram stimulus with 100 dots was used in this study. The Observer‟s task was to discriminate rightward and leftward translation, clockwise and anti-clockwise rotation and expanding and contracting radial optic flow patterns. Results: Children showed a reliable improvement in radial MCT with age, at both speeds. Surprisingly, the radial MCT of 16-year-old children did not reach the adult level, although it was closer to the adult value at the higher speed than at the lower speed (p<0.05). There was no significant difference in translational MCT for 8, 12 and 16-year-old children compared with adults. The adults showed better MCT for the higher than the lower speed, for all three optic flow patterns (p<0.05). MCT for translational flow was worse than MCT for the radial optic flow pattern at the lower speed (p<0.05) but similar at the higher speed (p>0.05). MCT was similar for a wide range of contrast levels and relatively high speeds in the pilot study. Conclusion: Sensitivity to radial optic flow develops with age. Younger children are poorer at detecting radial optic flow than older children and adults, with development continuing until late childhood. Sensitivity to translational MCT matures earlier. The development of radial MCT also differs with different stimulus speeds. Sensitivity to all optic flow patterns is greater at higher speeds. Sensitivity to the three optic flow patterns is similar at the higher speed but not at the lower speed. Differences in sensitivity to optic flow at lower and higher speeds, together with the varied development of radial optic flow at these speeds suggests that different motion perception channels are involved in processing slow and fast speeds.