I think it would help if you define what u mean by consciousness ?
Putting aside the causation controversy (brain or soul) I agree with Julian Jaynes when he start by defining what consciousness is not, like intelligence/intellect for instance.
Basically consciousness is what gives us will. Bicameral men possessed intellect but not will.
This intellect-will pair enables us to sustain a clearly internal dialogue. If you pay attention there are two distinct persons inside your mind (psychology defines as introversion and extroversion). And if you look closer there's a very subtle third person (because we are images of the Trinity) who observes the dialogue (this third person is very faded because original sin).
Bicameral men had only one person inside their minds. The second person was not only perceived as a voice but as an external image too. Jaynes says this image was seen as a kind of ghost.
With consciousness we lost this image and the voice became part of us and not an external entity.
But these internal people don't create ideas out of the blue. Complete ideas appear all the time and these internal persons discuss about deciding what ideas to keep.
Bicameral men received this ideas only by the external person and they couldn't decide to obey or not. We receive this ideas not from any internal person but from intuition that access the two sources of ideas.
We have the ability to decide upon these appearing ideas inside our minds.
Basically consciousness is the ability of decision (free will) by three internal persons in our minds about appearing ideas.
Consciousness is also an enhancer for all bicameral abilities.