How to explain the variation in so-called psychological invariants? The shift from psychophysical constancy to psychobiological adaptability

This paper outlines how the concept of psychophysical constancy entered int o cognitive psychology, by way of research into human memory, in the form o f so-called invariants. Such invariants have been conceptualised in differe nt ways as capacity parameters of human information processing. Empirical s tudies have shown, however, that parameters of this kind are subject to sys tematic variation. The possible reasons discussed here include, amongst oth ers, cultural influences. This contribution argues that where psychological processes are concerned principles of invariance can claim validity only o n an abstract level of explanation. This leads to a recommendation to place human adaptability in the centre of psychological research and thereby tak e into account characteristics of adaptive systems as explanatory principle s of human information processing.