Modules in spatial vision: implicit reasons of their functional attributes

Visual modules may also be viewed as expressions of a marked analytic attitude in the study of vision. In vision psychology they are accompanied by hypotheses of functional attributes, which characterize how they are thought to operate in perceptual processes. Our thesis here is that there are intrinsic reasons for the presence of such hypotheses in a vision theory; that is, reasons of a deductive kind, which are imposed by the partiality of the basic terms (input and output) in the definition of a module, and by peculiar characteristics of those terms. Specifically, we discuss three hypotheses of functional attributes: successive stages in the action of modules, residual indeterminacy of their effects, and the role of prior constraints. For each of the three, we indicate its occurrence in perceptual psychology, explain corresponding intrinsic reasons, and illustrate such reasons by examples.