The effect of non-adjacent luminance gradients on simultaneous lightness contrast

In this work we revisit a phenomenon presented by Agostini & Galmonte (2002), who showed an enhanced effect of simultaneous lightness contrast (SLC) by embedding targets within the glare effect and its photometric negative (Zavagno 1999). In our study we employed 3 manipulations of SLC with targets surrounded by non-adjacent positive luminance ramps (these determine the glare and dark hole effects), negative ramps (the vector of the gradient is inverted 180 deg), and solid black (white background) and white (black background) squares. Configurations with positive ramps show a strong contrast enhancement on both backgrounds with respect to classic SLC (data collected in a similar setup but with different subjects), in line with findings reported by Agostini & Galmonte. The magnitude of the effect is more than halved with negative gradients and solid squares. Findings are consistent with the hypothesis that luminance gradients are relevant information for brightness perception (illumination, luminosity).