Most imaginative people can imagine voices and often discuss things with themselves.
The acceptable version of Janes' hypothesis is that ancients attributed much of their imagination and interior life to objective reality.
A stronger version of Jayne's bicameral mind only requires that the ancient doubted ownership of certain of their emotions and trains of thought and discussed and wrote of them as real - the internal narrative, the train of thought, the stream of consciousness did not exist as a literary device and consequently the ancients did not possess it as a tool of thought.
As Gods and supernatural events were generally accepted in ancient times, the idea that internal dialogue was the voice of 'Gods' or deceased relatives was entirely reasonable as far as they knew back then.
The ancient might say the sea calls me home and the modern would understand the same emotion as guilt at not seeing ones parents.
Dreams are unbidden, uncontrolled internal imaginings we all have and anyone who stays awake long enough will start to hallucinate while awake.
Likewise stress and PTSD can induce unbidden thought, and uncontrolled imaginings and terrors.
We then attribute this to the unconscious mind, so we entertain a certain bicamerality.
Even so many of us moderns still entertain superstitions and use ritual to absolve ourselves from 'bad luck'. The Jungian hypothesis is that the unconscious responds to symbol and ritual and we require understanding our life course in heroic and mythic terms to properly become our own selves apart from our parents' views and social programming.
We are self aware enough to correlate certain cravings for particular sugary treats to advertising influencing us - is the desire for that product truly our own thought ?
We might say that a person lacks wit, empathy or is quick to anger - the ancient talks of them as under a planetary astrological influence or a symbolic event, a raven attending their birth, the reason for their behaviour - the same things are being communicated but the cause is differently attributed.
Jaynes proposes that minds were recently completely bicameral and did not posses our modern consciousness until bicamerality broke down - which is difficult to swallow, haven't we always been this human ?