There's a whole scientific study of consciousness that actually comes out of behaviorism. The thought is, if I have a conscious experience I can then exhibit the behavior of talking about it. From this developed a whole paradigm of investigation including stuff like the research of subliminal images.
Stanislas Dehaene's book Consciousness and the Brain does a great job of describing this, though it's 10 years old now.
Trouble is that you can also exhibit the behavior of talking about it just by being exposed to the idea, even if you don't have the experience. If you were never exposed to the idea and you started talking about it, then I'd be convinced you had the experience, but nobody is actually like that. The fact that the idea exists at all proves to me that at least one human somewhere had conscious experience, and I know there's at least one more (me), but that's it.
I was evidently unclear. I mean, if an image of a parakeet is flashed up on a screen for 100ms and you can say "I saw a parakeet" you were conscious of the image. If the image is flashed for 50 ms and you can't you weren't conscious of the image. In this paradigm being conscious is being conscious of particular things.
That seems like a fairly simple machine could be conscious, which is not usually how the word is used. Typically consciousness means that there is some ill-defined entity that has a subjective experience, what the philosophers call qualia.
Stanislas Dehaene's book Consciousness and the Brain does a great job of describing this, though it's 10 years old now.