The Master and His Emissary: The Divided Brain and the Making of the Western World
by Iain McGilchrist.
His [Julian Jaynes’] contention that the phenomena he describes came about because of a breakdown of the ‘bicameral’ mind – so that the two hemispheres, previously separate, now merged – is the precise inverse of what happened.
https://en.wikipedia.org/wiki/The_Master_and_His_Emissary
page 327
[Julian Jaynes’] insight that there was a connection between the voices of the gods and changes in the mental world of those who heard them, that this might have something to do with the brain, and indeed that it concerned the relationship between the hemispheres, remains, in my view, fundamentally correct. However, I believe he got one important aspect of the story back to front. His contention that the phenomena he describes came about because of a breakdown of the ‘bicameral’ mind – so that the two hemispheres, previously separate, now merged – is the precise inverse of what happened. The phenomena came about because of a relative separation of the two chambers, the two hemispheres. Phenomena that were previously uncomplicatedly experienced as part of a relatively unified consciousness now became alien.
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Putting it at its simplest, where Jaynes interprets the voices of the gods as being due to the disconcerting effects of the opening of a door between the hemispheres, so that the voices could for the first time be heard, I see them being due to the closing of the door, so that the voices of intuition now appear distant, ‘other’; familiar but alien, wise but uncanny – in a word, divine.
My thesis is that the separation of the hemispheres brought with it both advantages and disadvantages. It made possible a standing outside of the ‘natural’ frame of reference, the common-sense everyday way in which we see the world. In doing so it enabled us to build on that ‘necessary distance’ from the world and from ourselves, achieved originally by the frontal lobes, and gave us insight into things that otherwise we could not have seen, even making it possible for us to form deeper empathic connections with one another and with the world at large. The best example of this is the fascinating rise of drama in the Greek world, in which the thoughts and feelings of our selves and of others are apparently objectified, and yet returned to us as our own. A special sort of seeing arises, in which both distance and empathy are crucial.
But the separation also sowed the seeds of left-hemisphere isolationism, allowing the left hemisphere to work unchecked. At this stage in cultural history, the two hemispheres were still working largely together, and so the benefits outweighed by a long way the disadvantages, but the disadvantages became more apparent over time.
For the sake of simplicity, I will deal with the changes in more or less chronological order, beginning with what one might call the archaic period at least as far as the seventh century BC, moving on to consider the changes of the sixth and fifth centuries up to the time of Plato separately, and then dealing with the later period from Plato onwards.