Measuring the articulated-SLC in Virtual Reality conditions

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 perceptual lightness difference between these patches undergoes to a substantial augment when the two backgrounds – although maintaining the same luminance average – are patterned shaping what can be named the articulated-SLC. Two are the main interpretations of these phenomena. The layer approach claims that the visual system splits the luminance into separate overlapping layers, corresponding to separate physical contributions, whilst the framework approach maintains that the visual system groups the luminance within a set of contiguous frameworks. To contrast these two viewpoints in a psychophysics experiment run in Virtual Reality conditions, the articulated-SLC phenomenon has been measured by systematically manipulating the belongingness of pairs of luminance ratios sharing the same polarity. This is a crucial test because the two approaches make opposite predictions: According to the framework approach, the SLC should reduce when belongingness is increased (Gilchrist at al., 1999). On the contrary, according to the layer approach the SLC should increase when belongingness is increased (Soranzo & Agostini, 2006). Results show that the SLC increases when perceptual belongingness between the two frameworks is strengthened, supporting the layer approach to lightness perception.