If you want a rigorous account of what neuroscientists call consciousness, which isn't quite the same thing as what philosophers call consciousness, I'd recommend reading Consciousness and the Brain by Stanislas Dehaene. Looking at a brain, the reaction to stimulus that enters consciousness and stimulus that remains subliminal are very distinct. And, for example, only the effects of conscious stimulus persist in the brain for more than a couple of seconds. Well, Pavlovian conditioning between stimuli can occur subconsciously but only if the two two stimuli are presented at the same time. If you want to condition a dog to salivate when you ring a bell you either have to ring the bell loud enough for the dog to be conscious of it or you have to ring it while the dog is eating.