“Basically, Jaynes argues that consciousness, as we understand it today, has only been possessed by human beings for the last four thousand years or so. (By “consciousness” he means, not the primary perceptual awareness that all mammals, and perhaps many other ‘lower’ organisms as well, seem to possess, but what I would prefer to call self-consciousness, or second-order consciousness: the ability to reflect upon oneself, to introspect, to narrate one’s existence).
Jaynes proposes that, in the second millennium BC and before, human beings were not self-conscious, and did not reflect upon what they did; rather, people heard voices instructing them in what to do, and they obeyed these voices immediately and unreflectively.
These voices were believed (to the extent that “belief” is a relevant category in such circumstances) to be the voices of gods; their neurological cause was probably language issuing from the right hemisphere of the brain, and experienced hallucinatorily, and obeyed, by the left hemisphere (which is where speech is localized today).
This is why Jaynes calls the archaic mind a non-conscious, “bicameral” one. Thought was linguistic, but it did not have any correlates in consciousness; people didn’t make decisions, but instead the decisions were made automatically, and conveyed by the voices. One half of the brain commanded the other, so that decision-making and action were entirely separate functions. Neither of these hemispheres was “conscious” in the modern sense.
It was only as the result of catastrophic events in the second millennium BC that these voices fell silent, and were replaced by a new invention, that which we now know as self-conscious, reflective thought.
Jaynes introduces his theory by making reference to the Iliad, in which there is almost no description of interiority and subjectivity, or of conscious decision-making; instead, all the characters act at the promptings of the gods, who give them commands that they obey without question.”