Eighty postgraduate Psychology students, forty males and forty females, aged 19 to 22 years, served as Ss in a 2 X 2 X 2 factorial randomised group experimental design with a three-way classification of variables: duration of presentation, intensities of shock and sex. Two durations of presentations namely supra threshold of 0.50 sec. and sub-threshold of 0.20 sec. were used, 20 pairs of 7 syllable words, checked for ambiguity and familiarity, were presented singly through a camera shutter tachistoscope and simultaneously appropriate levels shock was also administered by a Dimmerstat. The immediate recall served as the index of vigilance. It was found that the duration of presentation significantly affected the coping strategy of vigilance and the intensity of shock worked differentially for the Ss of both the sexes. High intensity of shock was more vigilance evoking for male Ss whereas females gave better responses with low intensity of shock. The reduction of uncertainty was found to enhance perceptual vigilance. Theoretical reasons for these results have been discussed.