Stochastic resonance - the phenomenon whereby adding noise can make a signal easier to detect - can also be used to make the human eye more sensitive to light. Keiichi Kitajo of the University of Tokyo, Japan, and the University of British Columbia, Canada, and colleagues have shown that when exposed to a flickering random light, the eye can become sensitive to light at levels that would not otherwise be consciously detectable. The effect is the same even if only one eye tries to perceive the dim light while the flickering light is received by the other, so it is not simply a case of the eye "adding up" signals.
Further reading
K Kitajo et al. 2003 Phys. Rev. Lett. 90 218103.