Partial integration versus local/global anchoring: a test

In an earlier test between anchoring and intrinsic image models, Gilchrist et al. (1999) showed that when a middle-gray square in spotlight and a white square in ambient illumination are both placed on a large black paper, the middle-gray appears lighter than the white square. This result is in agreement with the anchoring model and contradicts the intrinsic image models predicting veridically perception. However, an intrinsic model with a classification failure of the illumination edge between the two squares (partial integration model) would also predict this outcome. To test between the anchoring and the partial integration model we repeated the test with an additional dark-gray square added to each framework of illumination. Partial integration predicts that both squares in the spotlight, the middle gray and the dark-gray, lighten by the same proportion, and that both squares in ambient illumination, the white and the dark-gray square, darken by the same proportion. The anchoring model, instead, predicts gamut compression, meaning that the dark-gray square in the spotlight lightens more than the middle-gray square and that the white square in ambient illumination darkens more than the dark-gray square. Results show strong gamut compression, supporting the anchoring model.