The role of perceived illumination in the articulated simultaneous lightness contrast.

The simultaneous lightness contrast (SLC) is the condition whereby a grey patch on a dark field appears lighter than an equal patch on a light filed. Interestingly, the perceptual lightness difference between these patches undergoes to a substantial augment when the two fields are articulated giving rise to the articulated-SLC, although maintaining the same luminance average. In this project two competing models explaining the articulated-SLC have been contrasted: the layer and the framework. The layer model claims that the articulated-SLC is due to the number of luminance pairs sharing the same polarity (Soranzo and Agostini, 2006 Perception & Psychophysics 68 102 - 113); whilst the framework model claims that it is caused by the difference in the highest luminance in the two fields (Gilchrist et al, 1999 Psychological Review 106 795 - 834). In a psychophysics experiment observers' lightness has been measured by systematically manipulating both the number of luminance pairs sharing the same polarity and the highest luminance in the two fields. Results show that the SLC persists even when the two backgrounds share the same anchor and its strength is inversely proportional to the pairs of luminance ratios sharing the same polarity, supporting the layer approach to lightness perception.