1. True External Voice -- Someone calls your name from behind you, you turn around and no-one is there.

2. True Internal Voice -- The same thing but it sounds as though the voice is inside your head.

3. Thought communication -- Think a thought question: "Shall I go to the party?" Answer the question with a thought answer: "Yes, I will, those interesting people will be there." Imagine that second thought does not feel as though it was generated by you.

In all cases it would seem as though distress would come if any of these communications occurred unbidden.

Interestingly, in this POS Biology paper (December 2013) on the social characteristics of voices there is this paragraph: 

The fact that voices stem from an internal source is, of course, clear, but the typical experience of “hearing voices” is not that thoughts seem to be “spoken aloud” but that hallucinated voices have a social identity with clear interpersonal relevance [2]. In other words, voices are as much hallucinated social identities as they are hallucinated words or sounds.

The question is: Is it clear? Where is the evidence that the voices stem from an internal source?

The similarities to the concepts of "telepathy" and "channelling" are immediate.

Comments welcome from experts.