Perception is direct pickup of invariants in the ambient optic array, not the processing of retinal images or the construction of representations. The animal and the environment are complementary; surfaces, media and substances are specified relative to the possibilities of action. Affordances are neither subjective values nor objective properties but ecological facts—what the environment offers the animal. Natural vision is ambulatory and ambient, not snapshot or aperture vision. The theory of information pickup dissolves the stimulus–response formula and the dualism of mind and body. Ecological optics replaces classical optics; the unit of analysis is the animal-environment system in continuous activity.
Uexküll, J. von (1956) Streifzüge durch die Umwelten von Tieren und Menschen.