Agostini and Galmonte (2002) 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.
