It is theorized that the mind was originally divided into an executive (the spirit world) and the follower (man). One part of the mind spoke to the other by audio hallucination. The notion is that there was an ancient bicameral mind that was not conscious or subjective in which the apparent spirit of a raven, a rock, or a burning bush could warn or instruct. This ancient mentality is demonstrated in comparison of earlier and later tablets of the Gilgamesh story, the Mycenean Iliad and later Greek literature, and earlier books of the bible, particularly Amos and Ecclesiastes. Each refers to direct communication with the gods without introspection, in a world before nature became an ecomachine. The bicameral mind was replaced with modern consciousness as civilization became more complicated, self-awareness has expelled man from the garden. Having lost the certainty of direct spiritual contact, religion set to work instituting the idea of a fall from divine favor. Its possible that the Comanches that were relatively isolated from Western consciousness that was beginning to pervade neighboring Indians, perhaps had still retained a bicameral mind and lived in the present, still free of the curse of self-reflective thought. Still open to the advice of an old oak. Unfortunately for the victims of Comanche raids, a nonconscious mind, with no subjectivity, did not register empathy.

Julian Jaynes. The Origin of Consciousness and the Breakdown of the Bicameral Mind, New York: Houghton Mifflin Company