DISCUSSION 

The present study showed that community home girls who had received physical training (CHP group) have significantly lower critical flicker fusion frequency (CFF), higher degree of optical illusion ("di") for "out trials", but not for "in trials", and lower right hand grip strength compared to girls of the same age who were staying at home and attending an ordinary school (SCH group). The community home girls who had received six months of training in yoga (CHY group) performed better i.e. higher CFF, 'lower "di" an "out trials" and marginally greater hand grip strength, than the CHP group, and were not significantly different from the SCH group. The data of the community home groups before they had learned yoga/physical training were not available. Hence the base line performance of these groups of subjects was not known. The hand grip is believed to be influenced by the availability of energy and oxidation requirement (12). 

The CFF has been correlated with factors such as physical stresses e. g. nutritional deficiency, fatigue during physical work, or sleep deprivation (4) as we11 as emotional stress (5). Greater stress levels have been correlated with lower CFF values. The "di" has also been correlated with cognitive factors such as the experience, hypotheses, and strategies of judgement (6). In the present study, the lower CFF values and higher "di" in the "physical activity" community home group could possibly be related to the higher stress levels, which earlier reports indicated that these subjects were specially likely to have (1, 2, 3). The CHY group did not have significantly different values for both CFF and "di" compared to SCH group. This could be related to the fact that the practice of yoga for short periods (10 to 30 days) has been shown to increase the CFF (7) and reduce optical illusion (8). The hand grip strength and tweezer dexterity scores did not differ significantly between the three groups using a single factor ANOVA. However, the 't' test for unpaired data showed a significantly lower right hand grip strength in the CHP group compared to SCH group. The absence of major differences between the groups for these two parameters could be explained in either of two ways, viz (i) the factors responsible for lower visual sensitivity (low CFF, high "di") in the CHP group of community home girls may not be applicable to grip strength/tweezer dexterity; (ii) alternatively, both yoga and increased physical activity may have been effective in the reducing adverse factors in the CHP and CHY groups with regard to grip strength or dexterity scores while there were still differences in CFF and "di". The grip strength and dexterity scores of the three groups hence appeared the same. The former explanation is contradicted by a very early report in the literature which describes poor performance in "asylum" children when hand grip strength and manual dexterity were tested (9). The latter explanation may be more acceptable. There are reports that the practice of yoga increases grip strength (10) and improves dexterity. A previous study has shown a comparable effect of yoga and physical training on grip strength and specific tanks requiring motor skills (11). This also may explain why no differences were observed between the two groups of community home girls for these two parameters, even though the CHP group had lower right hand grip strength than the SCH group. The physiological basis for the perception of optical illusion and of a flickering light stimulus are similar. In both cases changes at retinal, cortical and cognitive judgemental levels influence visual perception. However, in the case of flicker fusion, the peripheral visual pathway is specially important, and may be related to the frequency at which the optic tract discharges and to the discharge rate of "on-off" ganglion cells in response to an intermittent stimulus. Also in the perception of an optical illusion cognitive-judgemental factor are stressed (6).

The hand grip is believed to be influenced by the availability of energy and oxidation requirement (12). These factors may also be expected to influence the performance in a repetitive task requiring fine motor skills (i.e. the, dexterity test).

Hence the present study suggests that the reported higher stress levels in community home inmates reduced sensory perception by causing change at peripheral and central levels. To some extent yoga practice modifies this effect. Similarly muscle power (but not fine motor skill), was less in the community home group. Yoga practice also appeared to improve hand grip strength, perhaps by reducing the energy requirement. However, additional information on the baseline status of the community home group, prior to either training (which was not available in the present study) would be required to draw more definitive conclusions.