METHOD

Subjects

There were two groups (yoga and control) of 30 subjects each. The subjects of both groups were matched for age and sex, with ages ranging from 18 to 42 years (group average age ± SD, 28.8 ± 6.1 years) and 6 female subjects in each group. All subjects had normal vision without correction.

Apparatus

The degree of optical illusion was measured using the Muller-Lyer apparatus (Anand Agencies, Pune, India). The Muller-Lyer lines though of equal length, appear unequal due to the two different types of arrows drawn at both ends of the line: close-ended arrows making an acute angle or open-ended arrows making an obtuse angle with the shaft. In the apparatus used for the present study the line on the left was of fixed length and had close- ended arrows at either end giving it an illusory shorter appearance. In contrast the length of the line on the right could be varied. This line had open-ended arrows at either end which made it appear longer.

Assessment procedure

The experimenter manipulated the length of the line according to the subject's specifications. The exact position at which the subject perceived the two lines to be of equal length was noted, i.e. subjective reading ("sr"). The difference between the 'sr' and the reading at which the lines were actually of equal length, gave the degree of illusion ("di"). Each subject was assessed in two types of trials ('in' and 'out'), ten each, given alternately. For 'in' trials the examiner adjusted the length from maximum (200 mm) till the subject, seated 1.8 m away, perceived the length to be equal to the fixed line (160 mm). For 'out' trials the procedure was reverse, the adjustable line was kept to minimum length and the length was gradually increased till the subjects perceived the length to equal that of the fixed line. In both cases the difference (in mm) between actual length of the line and the perceived length was noted as the degree of illusion ("di").

Design of the study

Subjects of both groups were assessed at the beginning and end of a month. During the month subjects of the yoga group received training in yoga, whereas control group subjects carried on with their routine activities.

Yoga training

The yoga group received training in physical postures (asanas, 90 min), yoga voluntary regulated breathing (pranayama, 60 min), meditation (60 min), lectures on the theory of yoga (60 min), as well as visual cleansing exercises (trataka, 30 min). During trataka and meditation, subjects were given instructions to focus the gaze on a specified object, followed by defocusing. During asanas and pranayama practice subjects were asked to "focus" their attention (on their breathing or body sensations), followed by "defocusing".

Data analysis

The data were analyzed using the two factor ANOVA, where Factor A = Yoga versus Control group; Factor B = before versus after. Separate two factor ANOVA were performed for the data obtained during "in" and & "out" trials. The Tukey multiple comparison test was used to test for significant differences between group average values.