Mechanisms of modal and amodal interpolation

P. J. Kellman and T. F. Shipley (1992) and P. J. Kellman, P. Garrigan, and T. F. Shipley (2005) suggested that completion of partly occluded objects and illusory objects involve the same or similar mechanisms at critical stages of contour interpolation. B. L. Anderson, M. Singh, and R. W. Fleming and B. L. Anderson (2007) presented a number of arguments against this view. The author analyzes 3 of these arguments, as well as B. L. Anderson's ecological justification for believing that these mechanisms must be very different, and suggests that their conclusions are unwarranted. The author also outlines a model consistent with the identity hypothesis and with recent physiological evidence, including a quantitative proposal for contour interpolation strength. The model suggests that V1 and V2 receive from higher visual areas feedback that modulates their responses to stimuli eliciting modal completion, amodal completion, and collinear contour facilitation. The model qualitatively explains the unstable percepts evoked by various recently devised stimuli.