i say thatd it would take the form of a fabricated voice, because if you think about, it babies are unable to speak, and at very young age dont quite register every sound that they hear, however hey are still able to put thoughts together (although not as complex) and react accordingly... i imagine it works something like that, plus as the person would grow and gain more intelligence the ability to internalize would increase, and they would be able to put thoughts together in a simillar intelligent way... also i imagine through attempts at speaking throughout the years, and the registration of the vibrations through hier bodies of the voice, would give a rough idea as to the qualities of the person's own voice, which i imagine would help them fabricae the internalized voice... hope that helps