Luminance dependence of oscillatory dynamics in the human visual system

In a previous study, we showed that spatio-temporally localized supra-threshold stimuli generate oscillatory metacontrast masking functions. Based on a model of retino-cortical dynamics, we suggested that the oscillations in the metacontrast masking functions reflect intrinsic oscillations of cortical neuronal responses. In this paper, we examine how the oscillatory patterns in metacontrast masking functions depend on stimulus and background luminance. Our results show that the timing of the first three dips in the metacontrast function agrees well across the three observers in all conditions except for a dim stimulus on a bright background. For a bright background, there is a better agreement for the timing of the dips across the observers when the stimulus visibility is high. For a dim background, stimulus visibility does not affect significantly the agreement for dip locations among the observers. We suggest that the different pattern of results that we observed for early vs. late dips in the metacontrast masking function may be explained in terms of feed-forward vs. feedback signaling that depend more on exogenous vs. endogenous factors, respectively.