Gregory's main contribution to the discipline was in the development of cognitive psychology, in particular that of "Perception as hypotheses", an approach which had its origin in the work of Hermann von Helmholtz (1821-1894) and his student Wilhelm Wundt (1832-1920).
According to Gregory, Helmholtz should take the credit for realising that perception is not just a passive acceptance of stimuli, but an active process involving memory and other internal processes [REF].