Forty male and forty female postgraduate students served as subjects in a 2 x 2 x 2 x 2 factorial experiment. Twenty seven-letter paired meaningful stimulus words were tachistoscopically presented alongwith requisite shock inputs. Immediate recall served as the index of vigilance. The results showed that the degree of electric shock interacted with sex and that the exposure, expectation and sex also significantly interacted. The optimum levels of phasic arousal of male subjects were determined by their differential receptivity.