I think an important distinction is whether the response to stimulus is hardcoded or not, and the degree to which it's not. Saying simply 'stimulus-response' makes it sound like a reflex like pulling back your hand when you accidentally touch a hot plate. There's a world of difference between an automaton that always reacts the same way to a given stimulus on one end and on the other end a deeply learning mind that can store memories, create internal models to predict stimuli, maybe even 'rewire' itself to change what effects future stimuli can have. Sure, you could say that the latter just reacts to stimuli over a greater period of time (e.g. experience is just old stimuli still being reacted to) but to do so would be to gloss over the enormous difference in nature and complexity of such systems. And unless you believe in a metaphysical definition of consciousness, then somewhere in that complexity gap is where consciousness arises, so it seems hardly like something to be glossed over.