> Is the amount of chemistry, then, or length of signal transmission, the measure of consciousness?

Sure, but we're gonna limit ourselves to neurons and the degree of connectivity between them. A camera has none, QED. The more challenging comparison is between a comatose patient and one with locked-in syndrome: https://en.wikipedia.org/wiki/Locked-in_syndrome. There, we can't exactly come up with some 'an agent capable of sensing the world, and responding to changes in its environment' that an outside observer might use.