... my point rests on the fact that both the fully self-conscious person and the person in a vegetative state have an identical make up (excluding genetic difference etc) in their body, as opposed to a robot for example.
Similar make up, not identical. Even with hypothetical identical clones, the one in a vegetative state is not like the fully conscious one because of the physical differences that result in the vegetative state.
If the person in a vegetative state where to recover suddenly, one would know immediately that they where self-conscious and not just an automaton or robot. However if they where replaced by an automaton with the identical appearance of that person and behaved as that person did when they recovered, one would not be able to say, immediately, that they where self-conscious. Because they might actually be clockwork or some other mimicking device.
You could not tell
anything useful
immediately. You would
assume the recovered person to be self-conscious if they demonstrated behaviours consistent with self-consciousness over some reasonable period. However,
if, as you say, it is possible to exhibit those behaviours without being self-conscious (i.e. be a p-zombie), you could not be certain. The damage that caused the vegetative state might have made them a p-zombie (if you believe p-zombies are possible).
However, the point is not that you can tell immediately or even over an extended time that self-conscious behaviours are exhibited, but that
by definition they will be exhibited in
every relevant circumstance. And, yes,
if they actually were clockwork or some other mimicking device, and could show self-conscious behaviours indistinguishable from the human equivalent
in every circumstance, then it would be quite reasonable to say they were truly self-conscious. That's surely what 'true' self-consciousness means.
This is where the distinction between conscious and self-conscious becomes important. The machine which behaves in every circumstance as though it is self-conscious, need not be self-conscious to perform the act. All that it would require is a form of computation equivalent to a basic consciousness of its environment,*to succeed in its deception.
A basic consciousness of its environment would just be basic consciousness. It would not be able to display self-consciousness indistinguishable from human self-consciousness in every circumstance
because that capability requires self-consciousness.
To display self-consciousness indistinguishable from human self-consciousness in every circumstance, it would require more than a basic consciousness of its environment; such as a more sophisticated computational capability involving self-modelling. Perhaps
similar to that in humans.
An absolutely perfect mimicry is the thing it is mimicking.
If it quacks like a duck and it looks like a duck, it must be a duck and not an automaton.
Quacking like a duck and looking like a duck is hardly
perfect mimicry. The key concept is that the item being considered is
indistinguishable in every circumstance. For a whole duck, that would mean being a real duck; but you could probably replicate a real quack
