The role of physical contrast in Agostini & Galmonte's reversed lightness-induction Necker cube

Agostini and Galmonte (2002 Psychological Science 13 88 - 92) reported a configuration showing that when grouping factors are optimised, a grey target totally surrounded by black appears darker than an equal grey target totally surrounded by white. The theoretical assumption is that, when higher-level factors act simultaneously with lower-level factors, the former prevails over the latter. Specifically, it is assumed that the lightness induction produced by the global organisation principle of perceptual belongingness prevails over retinal lateral inhibition. The aim of the present study was to test the hypothesis that lightness induction produced by perceptual grouping does depend on the physical contrast between induced and inducing elements. To test this hypothesis, we systematically manipulated, in a number of psychophysics experiments, the relative physical contrast among the regions forming the original Agostini and Galmonte configuration. Observers were asked to match the lightness of both the inducing and induced element on a Munsell scale. We found that lightness induction produced by perceptual organisation principles depends on relative physical contrast between the induced and the inducing elements. Results are interpreted in accordance with previous studies on the relationship between lightness induction and physical contrast.