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Abstract:
Previous research has shown that the visual systems sensitivity to variations in luminance (visual contrast) within a particular area of the retina is affected by the ambient contrast levels in nearby regions in a bottom-up fashion. Specifically changes in the ambient contrast in areas surrounding the target area alter the sensitivity to visual contrast within the target area. More recently, it has been shown that paying attention to the target or target area modulates contrast sensitivity suggesting a top-down influence over contrast sensitivity that is mediated by attention. Here we report another form of top-down influence over contrast sensitivity that is unlikely to be mediated by attention. In particular, we show that knowledge and/or expectations about the levels of visual contrast that may appear in upcoming targets also affects how sensitive the observer is to the contrast in the target. This sort of knowledge-driven, top-down contrast sensitivity control could be used to preset the visual system
s contrast sensitivity to maximize discriminability and to protect contrast-sensitive processes from a contrast-overload. Overall, our results suggest that existing models of contrast sensitivity might benefit from the inclusion of top-down control mechanisms.
