Photometric relationships affect the simultaneous lightness contrast phenomenon in virtual reality

The simultaneous lightness contrast (SLC) is the condition whereby a grey patch on a dark background appears lighter than an equal patch on a light background. Interestingly, the lightness difference between the grey patches increases when the two backgrounds—although kept at the same luminance average—are patterned shaping what can be named the articulated-SLC. There are two main interpretations for these phenomena. The framework approach maintains that the visual system groups the luminance within a set of contiguous frameworks; whilst the layer approach claims that the visual system splits the luminance into separate overlapping layers, corresponding to separate physical contributions. To contrast these viewpoints in a psychophysics experiment run in a virtual reality cave, the articulated-SLC has been measured by systematically manipulating the belongingness among luminance pairs sharing the same polarity. This is a crucial test because the two viewpoints make opposite predictions: According to the framework approach the SLC should reduce when belongingness is increased (Gilchrist et al, 1999 Psychological Review). According to the layer approach the SLC should increase when belongingness is increased (Soranzo and Agostini, 2006 Perception & Psychophysics). Results show that the SLC increases when belongingness is increased, supporting the layer approach to lightness perception.