Agostini and Galmonte (submitted), Bressan (in press), and Economou, Annan, and Gilchrist [1998 Investigative Ophthalmology & Visual Science 39(4) S857] reported three different configurations showing that when grouping factors are optimised, a gray target totally surrounded by black can appear darker than an equal gray target surrounded by white. The common theoretical assumption is that, when higher-level factors act contemporaneously with lower-level factors, the contrast effect induced by the global organisation principle of perceptual belongingness prevails on retinal lateral inhibition. However, spatial frequencies of Bressan and Economou et al displays suggest an alternative interpretation. In a number of variations of their configurations, we observed that the direction of the effect does not change even in absence of global grouping factors. Our observations suggest that their results can be explained according to a mechanism of spatial summation eliciting lightness assimilation (adaptation-level theory) rather than to the principle of perceptual belongingness. This hypothesis is further supported by the observation that their illusion increases with viewing distance.
Contrast or Assimilation? Two ambiguous cases
GALMONTE, Alessandra
2001-01-01
Abstract
Agostini and Galmonte (submitted), Bressan (in press), and Economou, Annan, and Gilchrist [1998 Investigative Ophthalmology & Visual Science 39(4) S857] reported three different configurations showing that when grouping factors are optimised, a gray target totally surrounded by black can appear darker than an equal gray target surrounded by white. The common theoretical assumption is that, when higher-level factors act contemporaneously with lower-level factors, the contrast effect induced by the global organisation principle of perceptual belongingness prevails on retinal lateral inhibition. However, spatial frequencies of Bressan and Economou et al displays suggest an alternative interpretation. In a number of variations of their configurations, we observed that the direction of the effect does not change even in absence of global grouping factors. Our observations suggest that their results can be explained according to a mechanism of spatial summation eliciting lightness assimilation (adaptation-level theory) rather than to the principle of perceptual belongingness. This hypothesis is further supported by the observation that their illusion increases with viewing distance.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
