From Koffka's "invariants" to "networks of constraints". Implications of a concept from Gestalt theory

ABSTRACT: This is a conceptual analysis of "invariants" as meant by Koffka in his Principles of Gestalt psychology. First I highlight the set of terms and assumptions forming the logical background of an invariant and illustrate the concept by two examples (size-distance invariance hypothesis, gradient of whiteness). Then I consider the methodological use of Koffka’s invariants concerning "indirect specification of perceptual contents", and suggest that a generalisation of that use would lead to systems of psychophysical dependences which could be modelled as "networks of constraints" (as understood in information science and artificial intelligence theory). I exemplify this possibility by referring to the psychophysics of perceptual transparency, following Metelli’s approach to the problem.