The paper describes some experiments with a visual agnosia patient who has lost the abillity to perceive subjective contours. The patient's interpretations of simple examples of occlusion indicate that he fails to notice monocular occlusion clues, as well. The findings support the hypothesis that subjective countours are constructions that account for occluded figures, in the absence of objective edges. The patient's ability to perceive coutours by stereopsis demonstrates that stereopsis independently gives rise to disparity countours. Furthermore, the overall results strongly suggest that the detection of occlusion is modularized, and that the module for detecting
