I heard of this book over thirty years ago on the last day of my Ancient Mythology class in college, but have just recently read it after following some links about it from a discussion prompt for my Less Wrong meetup group.
Without having looked yet for contrary arguments, I provisionally find Jaynes's argument fairly persuasive. An extremely brief summary: from a variety of literary, historical, and archeological evidence, he suggests that the earliest civilized humans lacked consciousness in the sense of self-awareness or an inner life, and that volition, because it wasn't yet integrated with the externally acting part of the mind, consisted of remembrances of past admonitions from authority figures, was activated only by the stress of novel situations for which the individual lacked a conditioned reflex, and was experienced as a hallucinated voice as it was transmitted from one part of the brain to the other (hence the "bicameral" mind). An important part of the argument consists of explaining the gods of early civilizations as cultural interpretations of these voices, beginning with ascribing them to dead ancestors who had been the actual models for the hallucinatory voices before they died. Another part of the argument looks at reports from clinical or experimental subjects of electrical brain stimulation suggesting the existence of residual brain anatomy from a past bicameral period that may underlie aspects of such present-day phenomena as hypnosis and schizophrenia.
The first passage prompting me to comment is on p.29 (first Mariner Books edition, trade, 2000), where Jaynes is enumerating and debunking arguments for the necessity of consciousness for various functions, so as to render more credible the idea that early civilizations could have functioned without it. Here he's refuting the idea that consciousness is a "copy of experience," as follows:
Think, if you will, of when you entered the room you are now in and when you picked up this book. Introspect upon it and then ask the question: are the images of which you have copies the actual sensory fields as you came in and sat down and began reading? Don't you have an image of yourself coming through one of the doors, perhaps even a bird's-eye view of one of the entrances, and then perhaps vaguely see yourself sitting down and picking up the book? Things which you have never experienced except in this introspection!
After a couple similar examples, he concludes,
Looking back into memory, then, is a great deal invention, seeing yourself as others see you.My own answers to the two questions just quoted are in fact, most definitely, "Yes" and "No," respectively, contrary to what Jaynes confidently expects. In fact, prior to 2002, I would have been surprised to learn that anyone remembers ter experiences from a third-person vantage point, as Jaynes seems to assume everyone does.
That was the year I read Susan Blackmore's book Dying to Live: Near Death Experiences. As part of her effort at a naturalistic explanation for this phenomenon, she considers out-of-body experiences more generally, and discusses the fact that while some people imagine or remember their actions from a first-person perspective, others form a third-person mental image. IIRC, she cites evidence that which disposition a person has is predictive of ter likelihood of having an OBE -- specifically, that the latter are far more likely to.
So, the only somewhat surprising thing here is that a professional psychologist who'd already been in the field many years when he completed this book, was just as ignorant of the diversity of human minds in this respect as was I, who only took a couple college courses in the subject. I suppose this is an example of what's sometimes called the "typical mind fallacy," as discussed here: http://slatestarcodex.com/2014/03/17/what-universal-human-experiences-are-you-missing-without-realizing-it/
That being said, the fact that what Jaynes writes here is true of even some of us does make his case quite strong, as do many other arguments in that section of the book.
After making his case about things he thinks consciousness isn't, Jaynes follows with an explanation of what he thinks it is: essentially, that it's a particular system of metaphors constructed by means of language. In fact, he holds that metaphor "is the very constitutive ground of language," and argues that "[i]n early times, language and its referents climbed up from the concrete to the abstract on the steps of metaphors, even, we may say, created the abstract on the bases of metaphors."
This rang a note of familiarity for me, because it echoed a thought I'd had about the first substantial book I ever read: The Phantom Tollbooth, by Norton Juster. I've pondered why I started becoming so intellectual from an early age, and it occurred to me that this book, which I loved when I read it at age eight, is very well suited to preparing you for abstract thought, because it largely revolves around depicting abstracts as concretes in a fun way. If what Jaynes argues here is true, such depiction isn't merely helpful, but essential to thinking abstractly.
In his discussion on the significance of oracles, Jaynes writes about Delphi (p. 323):
Another kind of explanation, really a quasi-explanation, still busied about with in the popular and sometimes professional literature, is biochemical. The trances were real, it says, but caused by vapors of some sort rising from a casium beneath the floor of the cave. But the French excavations of 1903 and more recent ones have shown distinctly that no such casium existed.
I'd also been told of this "quasi-explanation" and subsequently that it had been debunked. But in 2001 I heard about this discovery: http://news.nationalgeographic.com/news/2001/08/0814_delphioracle.html. So, it appears vapors may well have induced the Pythia's ravings after all. This isn't inconsistent with Jaynes's idea, however; in fact, by calling it a "quasi-explanation," he's indicating that, even if vapors were the trigger, the particular form of behavior they induced must have been enabled by some kind of structure in the brain, for whose origins his hypothesis offers an explanation.
Finally, on page 394:
The hypnotic phenomena found in a medical psychiatric setting are commonly more profound, because, I suggest, a psychiatrist is a more godlike figure to his patient than is an investigator to his subject. And a similar explanation can be made for the age at which hypnosis is most easily done. Hypnotic susceptibility is at its peak between the ages of eight and ten,
adding in a footnote,
In a forthcoming book, I shall be discussing the development of consciousness in the child, suggesting that this age of greatest hypnotic susceptibility is just after the full development of consciousness.
Jaynes never published the above-mentioned book, and I don't know whether he presented supporting evidence for this suggestion in some other form. But this rang another bell for me, because I distinctly remember that at age eight, I started having the feeling that this time in my life was special in some undefinable way because I was different from how I'd been before. All I could articulate (in my own mind; I don't remember mentioning it to anyone else at the time) was that it had something to do with my mind. I was aware that I was starting to shoot ahead of my peers scholastically; things that they all seemed to struggle with, like multiplication and division, were old hat to me. But the feeling of difference was more intrinsic, about how I had changed, not merely a comparison with my peers. After reading the passage quoted above, I suspect the hard-to-define change of which I was self-aware at that age was, after all, simply the fact that I was self-aware, whereas I hadn't been before, at least not fully.
At the Less Wrong meetup the other day, I asked the two others present if they had a similar memory, but neither did. Perhaps the difference lies in the emotional role that abstraction assumed for me at that age. The family situation felt rather chaotic: when I was seven Father was working out of state and we only got to see him on weekends. Around my eighth birthday (IIRC) we moved again, and within 12-18 months we were reduced to being tenants in a couple rooms of the house, but I'd picked up on the fact we were struggling with the mortgage even before that happened. In this context, as I've reflected previously, discovering a mental world where things were orderly and predictable (numbers, especially) provided a great refuge.
When Brian Martin's death was announced on the news a few days ago, the anchor asked, "What's your favorite Beatles song? Could be a tough question, I guess." I immediately agreed, but just a moment later started thinking of one: "Strawberry Fields." And as soon as I did, I had an idea why: I vaguely remember listening to it in the "music room" where the stereo was, relating it to the feeling of having a space inside myself where everything was peaceful and calm. And it now seems to me that the sense that I was different now was important because it was linked to having a "mind-space," as Jaynes would put it, where I now could go to find a rational and orderly world.