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DISCUSSION
Yoga training of children for 10 days resulted in a significant improvement in, visual perceptual sensitivity as measured through Critical Flicker Fusion Frequency and the degree of optical illusion. The control group who did not receive yoga showed no change.
Table 1 Group Mean Values of CFF and Degree of Illusion ("di") for both In and Out Trials ± SEM of Yoga and Control Groups on Day 1 and Day 10
 Previous studies on adults with varying durations of yoga training showed improved visual perception (Ramana et al., 1997; Telles et al., 1997). There was a graded increase in CFF on days 20 (11.16%) and 30 (14.96%) as compared to day 10 (9.2%). The present study showed similar percentage of improvement in CFF (9.2%) after 10 days, as compared to the previous study (Ramana et al., 1997), and was statistically significant. The increased CFF following yoga could be attributed to the effects of yoga in reducing physiological signs of stress, such as decrease in heart and breath rate and in oxygen consumption (Joseph et al., 1981), as CFF was found to be lower during specific stressors, such as food and water deprivation (Ali & Amir, 1989). The non-significant improvement in CFF in the previous study on Day 10 as compared to another study (Telles et al., 1995), which showed a significant improvement on Day 10, was correlated to the difference in their age groups. The subjects of the former study were of the age group 25-39 years while the latter study had subjects of 17-22 year age group. Hence the significant changes in CFF in the present study suggests that younger age group could improve in performance following a shorter duration of yoga, compared to older subjects.
A previous report on optical illusion suggests that one month of yoga brings about an 86.2% decrease in the degree of illusion perceived (Telles et al., 1997). The present study in children following 10 days of yoga also showed similar results, but was of lesser magnitude (27.9 %).
The decrease in the degree of illusion perceived over a short period would be mainly due to cognitive judgemental factors, but not retinal or cortical factors as generally understood (Coren & Girgus, 1973). The cognitive judgmental factors involve the way in which the subject interprets incoming visual information based on experience, hypothesis and strategies of judgement. Hence the training through yoga to focus and defocus might have influenced the cognitive judgmental factors of the subjects, to significantly reduce the degree of illusion perceived.
Hence yoga training showed improvement in the subjects visual perceptual sensitivity. The present study suggests that younger subjects can show better improvement in performance following yoga training of a relatively short duration.
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