In natural vision, due to object, body, head, and eye movements, the contrast and orientation information received by our eyes change simultaneously and rapidly, yet our visual system can efficiently and accurately distinguish the contrasts and orientations under the dynamical conditions. The visual processes responsible for discriminating orientations and contrasts occurred at this very short time scale, however, are poorly understood. In the current experiments, we investigated the ability of human subjects to discriminate orientations or contrasts using the briefly presented stimuli in which orientations and contrasts were changing simultaneously in comparison with the stimuli in which orientation changes were discriminated when contrast remained constant or contrast changes were discriminated when orientation was constant. We show that the discrimination threshold for orientation or contrast when both contrast and orientation were varying was significantly lower than that for orientation when contrast was fixed or than that for contrast when orientation was fixed. Moreover, the decreased magnitude of discrimination thresholds to orientation or contrast was negatively correlated to the discrimination threshold to orientation or contrast when only orientation or only contrast was varied. These results indicate that the simultaneous changes in orientation and contrast enhanced the discriminability of subjects to contrast and orientation. The subjects who had lower discriminability to orientation or contrast when only orientation or contrast was changing had a relatively larger enhancement in their ability to discriminate contrasts and orientations when both orientation and contrast were changing simultaneously. We suggest that human visual system is more efficient at discriminating orientation and contrast when both parameters are changing which often occurs in natural environments. Our study sheds light on the underlying visual processes.