Thanks DSimon.
Coming from an evolutionary psychological point of view, Julian Jayne's theory consciousness being a by product of language comes to mind.
JJ also looks at historical consciousness and points out how it seems to be different to ours, especially when we look at ancient art and the writings of the Illiad.
The art of the ancient Egyptians and Mayans is also so radically different, I think it suggest differing levels of consciousness. Only when you are on that level can you perhaps decipher it. Much like you cannot access memories of early childhood - I think this is to do with a different level of consciousness.