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VERS.10 7Feb. The bicameral mind or bicamerality, as conceived in the Bicameral Hypothesis proposed by research psychologist Julian Jaynes, was the "preconscious" social and mental system of the world's first civilizations and religions. It was, as a product of evolution, a "primitive" functioning of the human brain and ancient humanity's "method of behavioral control" with a "mentality based on verbal hallucinations". It is called (i.e. "two-chambered") because the hallucinations, as hypothesized, were generated by the right cerebral hemisphere and 'heard' by the left as if spoken, providing a mental system in two parts — an executive authority and a human follower — without consciousness; and in certain contexts the "executive part [was] called a god". In other words, 'bicameral humans', like people today, had sensations, could communicate, and usually acted habitually, but unlike today, they had no 'mind' or 'inner self' and could not reflect on their own actions and experiences; instead, an ancient human would regularly hear and automatically obey an hallucinated 'voice', or 'voices', which commanded action. The 'voices' expressed the right hemisphere's accumulated "admonitory experience" which was activated simply by stress or by hallucinogenic sounds, sights and ritual aids. In all early civilizations everyone heard such 'voices' which were recognized as the authoritative "voices of chiefs, rulers or the gods[.]"

Jaynes (1920-1997) proposed the bicameral hypothesis in his book The Origin of Consciousness in the Breakdown of the Bicameral Mind which came out in January, 1977 and presents a wide range of supportive evidence found largely, according to Jaynes, "in the literature and [archaeological] artifacts of antiquity." Bicamerality is understandable only in the context of the book's overall psycho-historical theory which involves two additional hypotheses: the first explains that consciousness is the second, that  On this account, consciousness was a "new mentality" that became possible "only after the breakdown" of bicameral mentality, and since the middle of the 1st millenium BCE, consciousness has flourished and interacted with "the rest of cognition" to expand human abilities and reshape human culture. Meanwhile, the preconscious mentality has left a cultural legacy, especially in religious traditions.

All the hypotheses together potentially explain many "otherwise mysterious facts", of ancient history and of the modern world that might be based on functions of the right cerebral hemisphere. Many such phenomena, as possible "vestiges" of bicamerality, have varying degrees of "diminished consciousness" (e.g. possession, hypnosis) while the hallucinations of severe schizophrenia might be a "partial relapse" to bicamerality, with a possible genetic basis.

The bicameral hypothesis has been influential, having "inspired much of the modern research into hallucinations in the normal population [since] the early 1980s[.]" The phenomenon of voice-hearing nevertheless remains poorly understood both neurologically and historically. It is reported in most, and possibly all, cultures, often with a religious or spiritual significance, and is not necessarily a sign of mental illness, which motivates individuals, and groups such as the Hearing Voices Movement, to seek significance in the experience. Jaynes’s hypotheses are highly controversial: his method involved "bold" speculations and his use of ancient texts as evidence cannot be scientifically conclusive; moreover, the bicameral hypothesis is largely unproveable while it challenges commonplace assumptions and deeply-held convictions about human nature, mental health, and religion. Among early critics of Jaynes’s proposals, "everyone could find a topic or conjecture that they disagreed with" or they found the theory "ingenious [and] remarkable", yet also "exasperating [in its] incompleteness". Among detractors, one early objection was that Jaynes's position is patently "absurd", another was that his theory is attractive only to people with certain biases. Supporters — who acknowledge that "Jaynes’s work is generally dismissed" or is mostly "ignored" by experts in one or another discipline — contend, nevertheless, that Jaynes’s theorizing "continues to be ahead of much of the current thinking in consciousness studies" and that "the vast majority of critiques of the theory are based on misconceptions about what Jaynes actually said[.]"

Implications and significance
If the bicameral hypothesis is correct, it has many, "far-reaching" implications, including:
 * the evolution of language involved both sides of the brain, and the organization of language in the brain is changeable;
 * bicameral verbal hallucinations "may have evolved by natural selection as a method of behavioral control" within small groups, enabling the system of social control and organization of the first agricultural civilizations wherever they arose;
 * bicamerality also inspired "our first ideas of gods" as evident in the polytheism, idolatry, and theocracy of ancient societies worldwide;
 * the "weakening" of bicameral authority, possibly by the invention of writing, can explain the increasing frequency of references and images during the 2nd millennium BCE of 'supernatural' demons, angels, and ghosts, etc. which served as "hybrid human-animal" intermediaries to the gods; these were followed increasingly by 'spiritualistic' and 'magical' practices, such as divination, incantation of spells, amulets, prayers, and oracles, etc., all aimed at invoking, appeasing or replacing the "absent" or unreliable gods;
 * the varied "vestiges of the bicameral mind" comprise "a large class of phenomena of diminished consciousness" that may crucially involve "right hemisphere function in a way that is different from ordinary conscious life" and may in some cases involve "a partial periodic right hemisphere dominance". Although they need not involve hallucination, such vestiges generally involve some degree of trance. Examples are: music and poetry; prophecy, spiritual possession, and glossolalia; hypnosis; shamanism and "the 'invisible playmates' of childhood; [...] and hundreds more."


 * behavior that aims to satisfy a psychological quest for certainty, sometimes in service to a 'higher power', may be explained as a need for "archaic authorization" that is supported by a social process described as the.
 * the need for self-control, morality and personal responsibility may lie in the loss of automatic obedience to bicameral voices: "[...] voices which had to be obeyed were the absolute prerequisite to the conscious stage of mind in which it is the self that is responsible and can debate within itself, can order and direct, [and] the creation of such a self is the product of culture."

The final chapter of Jaynes’s book is an essay in which he interprets the "drama . . . of the central intellectual tendency of world history[,]" the on-going trend of human culture moving away from its bicamerally religious foundations: this tendency is expressed in "the urgency behind mankind’s yearning for divine certainties." For Jaynes, the move towards a "secularization of science" is an expression of the "erosion of the religious view of man [that has been and] is still a part of the breakdown of the bicameral mind." Jaynes argues that the modern pursuit of science is also a search for certainties in "response" to the breakdown. He asks, "Why should we demand that the universe make itself clear to us? Why do we care?" In 1978, interviewer Richard Rhodes quoted Jaynes, as follows, on the historical relationship between bicamerality and religion: "One of the things I’m trying to protect, […] by identifying its sources, is the function of religion in the world today. The voices are silent. True. But the brain is organized in a religious fashion. Our mentalities have come out of a divine kind of mind."

Foundations of the hypothesis
Ideas from four different areas of research inspired and justified the hypothesis of the bicameral mind: 1) consciousness — the ability to introspect — is distinct from biological processes of cognition; it is absent far more than is commonly supposed, is not at all necessary for most human behavior, and is a product not of biological evolution but of language and culture; 2) ancient texts and archeology indicate that consciousness may be no more than 3000 years old and, for several thousand years earlier, the historical record indicates the existence of a different mentality which was in some ways similar to hallucinatory aspects of modern schizophrenia; 3) verbal hallucinations, which in recent centuries have been socially and medically problematic, must have a neurological basis, yet as of the 1970s were unexplained by modern science; 4) mid-20th-century discoveries, particularly about brain plasticity and the apparent independence of the hemispheres in the so-called "split brain", generated new ideas about ordinary, altered and complementary "modes of consciousness" (e.g. propositional/appositional, verbal/visuospatial, analytic/holistic) possibly related to the "duality" of the cerebral hemispheres.

The possibility of a non-conscious mentality
Most people probably take it for granted that consciousness — the 'inner life' that is linked with ideas of the soul or mind — is simply 'human nature', "the most self-evident thing imaginable[,]" yet its nature and origin have long been problematic for philosophers, and for psychologists and biologists since at least the time of Charles Darwin. The idea that consciousness is not what it seems to be, and that humans could, and did, live without it, is not easy to explain or to understand. Experimental psychology in the 20th century has shown that much of human mentality, like the mentality of other animals, involves cognitive processes that are mostly automatic and habitual: perception, decision-making, and learning, for example, take place without any awareness of how they happen. One can, however, know that such processes exist and 'be conscious' of them when 'reflecting' on them. According to Jaynes, the phenomenon of consciousness — its functionality — is evident in the ability to introspect, that is, the ability to reflect on experience and behavior, and to reconstruct the past as it have been or to imagine past and future possibilities. Our mental activities certainly involve the brain, but nobody is ever conscious of their brain at work, nor can any amount of introspection reveal 'how' the brain works (i.e. nerve impulses, synapses, etc.). While most people describe their 'mental life' and private thought as taking place 'inside one's head', they mean the so-called 'inner world' of subjectivity, or as Jaynes puts it, one's "mind-space", and the language people use to describe the mind-space and its 'contents' is not the language that describes the brain; rather, the mind can only be described or talked about with words that normally describe the physical world. Jaynes puts it this way:"Every word we use to refer to mental events is a metaphor or analog of something in the behavioral world."

Jaynes explains further that it is through the use of metaphors that people feel that they anything at all, and he develops an original  that explains how metaphors allow people to assume the existence of a "mind-space inside our own heads as well as the heads of others[.]" As a result of doing so, people are able to understand and explain their own behavior and that of others as caused by something 'on the inside'.

Furthermore, if consciousness — with the mind-space that is its "primary feature" — is based on metaphoric aspects of language, it can only be a human ability, and it can emerge only at a certain level of social complexity. Therefore, says Jaynes, consciousness cannot be innate and cannot be necessary, and a society could have once existed with people "who spoke, judged, reasoned, solved problems" and more, without ever having learned to be conscious at all.

The 'mind' in ancient texts
Popular and scholarly translations of ancient texts are full of assumptions that ancient people were psychologically the same as we are today. The presence of consciousness in the past is self-evident when texts use vocabulary that is obviously mental, with words that clearly refer to the existence or acts of a person’s 'inner' being. However, in the oldest texts that can actually be understood the original meanings of such terms are concrete, referring to limbs, organs or bodily actions. Contrary to ordinary assumptions, no words for anything like 'the mind' are found at all in the oldest texts that are well-understood, not in Greek, and not in Hebrew, although they are increasingly abundant towards the middle of the 1st millennium BCE.

The gods of ancient Greece
The may be "the earliest writing […] in a language that [modern readers] can really comprehend[.]" Jaynes analyzes this earliest source of Greek mythology, emphasizing two points: first, that the original Homeric Greek had no mental vocabulary, in contrast to classical Greek hundreds of years later; secondly, the human heroes of the  are explicitly depicted as being driven into action by ‘gods’ who themselves took part in the action. Jaynes explains how these depictions are similar to many hallucinations reported by people diagnosed with psychosis. He concludes that the explicit ‘mythological’ content of the epic poem "suggests" an entirely new interpretation: that in the late Bronze Age and for centuries afterwards into the early Iron Age, the 'gods' were taken very seriously by those who recited and heard the heroic tales for the simple reason that the gods were generally experienced in the same hallucinatory way. The becomes for Jaynes "a psychological document of immense importance", providing an ancient clue to the hallucinatory mentality that he calls the "bicameral mind".

Hallucinations ancient and modern
Since the dawn of civilization human physiology and cognition have been fundamentally as they are today, and the ancients "moved through their lives on the basis of habit — just as we do" today. "[B]icameral beings knew what followed what and where they were, and had behavioral expectancies and sensory recognitions just as all mammals do[.]" Nevertheless, based on evidence from as late as the Bronze Age, although people had the ability to communicate with language, they had no obvious 'inner life'."Iliadic man did not have subjectivity as do we; he had no awareness of his awareness of the world, no internal mind-space to introspect upon."

The same evidence suggests that this preconscious era was also an era of 'voices', the character of which is similar to hallucinations reported by patients with psychosis. Among other relevant similarities, "... auditory hallucinations in general are not even slightly under the control of the individual [patient], but they are extremely susceptible to even the most innocuous suggestion from the total social circumstances of which the individual is a part. In other words, [...] hallucinations are dependent on the teachings and expectations of childhood — as we have postulated was true in bicameral times."

Even though they occur within the individual's brain, hallucinated voices sound and seem as 'real' as any human voice. When an ancient, non-conscious individual 'heard a voice' making an authoritative command, the command could not be disobeyed because it expressed the brain's (i.e. the individual's) unconscious volition, and volition was itself conditioned by childhood experiences and the general social order.

The bicameral interpretation of the ancient evidence notes that every early (bicameral) society had a clear hierarchic order in which everybody relied on the voices of authority, whether real or hallucinated, that told an individual what to do. Bicameral people differed, however, from modern voice-hearers and the schizophrenic patient "living with hallucinations that are unacceptable and denied as unreal" by others: bicamerals, lacking consciousness, could neither 'see for themselves' nor, for lack of an 'inner self', could they 'tell themselves' what to do; and, for lack of a culture of consciousness, they could not have deduced, imagined or even made sense of the idea that such voices 'came from their own heads'.

In the modern world, the 'hearing of voices' is not necessarily a disorder or disease, and the phenomenon and its reception is highly dependent on the cultural context in which it occurs.

Pre-historic graves and idols
Verbal hallucinations "may have evolved by natural selection as a method of behavioral control" as a result of the evolution of groups and the evolution of language. Pre-historic human groups were small, and the first bicameral voices could have been the hallucinated echoes of the voices of parents or group leaders who, after they had died, would be regarded as still living if they were still being 'heard'. Such an experience can explain the origin, as early as 9000 BCE, of certain ceremonial treatments of the dead: for example, of burial beneath the home (as at Tel Jericho), of Paleolithic skull cults that severed the head from a corpse and preserved the skull (as at Göbekli Tepe), and of "double burial of the same corpse" (perhaps after the 'voices' had stopped). Elaborate mummification rituals, for thousands of years and in widely separated parts of the world, preserved physically dead bodies for their afterlife. Similarly, simple burial mounds used for millennia around the world, in some places evolved into complex tombs in the extravagant form of the ancient pyramid which served also as the "god-house", a center of social life focused on the continuity of a "god-king's" afterlife activity. Although ancient civilizations differed one from another for various reasons, they also shared significant similarities. Archaeology has uncovered considerable evidence of polytheism, and of theocratic societies dominated by authoritarian gods. Almost all early settlements had a place of some kind for statuary: in some cases "shrines" were located in personal dwellings (e.g. 7th-6th millennium Çatal Hüyük); more conspicuously, some large settlements not built around a tomb had a communal, centrally located temple, or god-house (e.g. 7th millennium Tel Jericho, or the later ziggurats of Ur) in which statuary gods could rule for generations in place of a ruler's corpse. Many of the oldest artifacts are strangely formed figurines, statues and cultic images, thousands of them small enough to hold in the hand. The bicameral hypothesis explains that many such figurines, and perhaps the monumental architecture as well, served as hallucinogenic devices that stimulated the 'hearing' of voices to manage behavior.

An era of cultural and mental transition
Differences between older and later texts of Ancient Mesopotamia, Ancient Greece, and the Hebrew Bible suggest that events late in the 2nd millennium BCE, perhaps between 1400 and 1200 BCE, were of profound importance, not only for advances in technology but for the history of the human mind. The epoch is marked by the 'Late Bronze Age collapse'. Among the Greeks, this collapse preceded the so-called 'Greek Dark Age' which was in turn followed by the well-documented revival of culture known as classical Greece. Among the Hebrews, traditions, legends and historical events that were compiled and finally canonized into the scriptural books of Judaism recount "the mental struggle that followed the breakdown of the bicameral mind."

The latter part of this era has independently been interpreted by some historians as particularly significant without any reference to the bicameral hypothesis: Karl Jaspers called it the "axial age" of the 1st millennium BCE, which parallels what Bruno Snell called the era of the Greek "Discovery of Mind". Inspired by the bicameral hypothesis, scholarship aimed at the "tracking of ancient mentalities" has helped to explain Chinese funerary practices from a period "approximately the same as in Greece".

The bicameral interpretation of evidence from those centuries sees a major change of mentality, from the social order dominated by (hallucinated) gods and spirits to the emergence of a society of newly-conscious humans struggling, philosophically, to the world and their place in it: it was the period "when so much of what we regard as modern psychology and personality was being formed for the first time." As individuals began to learn conscious behaviors, whether in response to social collapse or by encounters with conscious others, the ability took hold and spread, quickly in some places, slowly in others, while the religious legacy of bicameral society could adapt only gradually.

Irrationality in classical antiquity
Numerous classical texts reveal varying attitudes of conscious people towards phenomena that can be explained as early vestiges of lost bicamerality. For example, even as the culture of philosophy and rationality took hold in classical Greece and Rome, the highest poetry was that composed "in a state of frenzy", and religious ecstasy was early on regarded as the "divine gift" of madness. Even the philosopher Socrates had his "daimonion" (personal deity). Jaynes describes a well-known passage from Plato:

"In the Phaedrus, Plato calls insanity 'a divine gift, and the source of the chiefest blessings granted to men.'[Phaedrus, 244A] And this passage preludes one of the most beautiful and soaring passages in all the Dialogues in which four types of insanity are distinguished: prophetic madness due to Apollo, ritual madness due to Dionysus, the poetic madness 'of those who are possessed by the Muses, which taking hold of the delicate and virgin soul, and there inspiring frenzy, awaken lyrical and all other numbers,' and, finally, erotic madness due to Eros and Aphrodite."

The books of the Hebrew Bible recount the early conflicts between 'true' prophets ("nabiim") and 'false' prophets, while in later centuries, according to Abraham Heschel, the Talmudic tradition held that "the absence of ecstasy is the mark that distinguished the Hebrew prophets from all other prophets." Heschel explains:

"The rabbis looked with irony upon the phenomena of wild ecstasy which were common in Palestine and Syria in the third century C.E. ... [and] in the sayings of Rabbi Yohanan (d. C.E. 279), who was the head of the leading academy in Tiberias, Palestine: 'From the day of the destruction of the Temple prophetic inspiration was taken away from the prophets and given to children and madmen.'" The bicameral hypothesis interprets the older prophets, who always knew what their 'voices' said, as closer to original bicamerality than the later ecstatics, who displayed "a complete domination of the person and his speech by the god-side, a domination which speaks through the person but does not allow him to remember what has happened afterwards. This phenomenon is known as possession." A similiar analysis applies to the "Age of Oracles" and sibyls among the Greeks, which passed through several stages, degenerating from their original simple function of inspiring 'voices' into their later ecstatic and erratic forms, sometimes with outright fakery. Nevertheless, pagan "oracles were the central method of making important decisions for over a thousand years after the breakdown of the bicameral mind[,]" but as they approached their eventual disappearance during the 4th century CE, they increasingly became targets of mockery by the growing community of the conscious.

Language and the brain
When the hypothesis was proposed, the tools to investigate language processes in the brain were limited, and the prevailing neurological model at the time emphasized the 'dominance' of one hemisphere. Today the language system is known to be more complex than the 20th century 'classical model' proposed, and the right hemisphere has a distinctive role in successful linguistic and non-linguistic communication. Meanwhile, no single model explains the neurology of verbal hallucinations, and the right hemisphere's role in the phenomena remains controversial. While auditory hallucinations might not all be explained by the neuropsychological model proposed for bicameral 'voices', an "abnormal asymmetry" involving more than "normal" right hemisphere activity might account for the distressful voices symptomatic of severe schizophrenia.

A "preposterous" proposal
Julian Jaynes was a respected lecturer and researcher in psychology at Princeton University from 1964 to 1995, and his only book, The Origin of Consciousness in the Breakdown of the Bicameral Mind, was written for general readers. It presented "his lifelong work" on the problem of consciousness. Jaynes's arguments were complex and original, drawing evidence from a "staggering" range of subjects, and his conclusions were called "ingenious" and "remarkable", yet also "exasperating". Jaynes recognized that the idea of the bicameral mind was so obviously contrary to widely-held beliefs about human nature that, in anticipation of readers' reactions, he himself characterized it as a "preposterous" idea. David Stove wrote in 1989 that Jaynes's "controversial and provocative" theory was "that rarest of things: an absolutely original idea…of most various and far-reaching consequences[.]" Regarding bicamerality, Stove commented that "…if such a thing had happened, an astounding number of otherwise mysterious facts would receive an explanation!" and Stove added that "Jaynes has made a definite suggestion, where no one else had a single thing to offer" to explain the existence of religion.

Radical, speculative and complex
Richard Rhodes commented in 1978: "Jaynes's theories…are radical, though well within the traditions of science — he is no Velikovsky or von Daniken bending the facts to sweeten preconception." In 1986, Daniel Dennett argued in defense of Jaynes that he had sought to maintain "plausibility" acceptable to scientific standards, even though his project was a necessarily "bold" and "speculative exercise" to fill unavoidable gaps in the historical data. It risked the "dangers" of making huge mistakes because it combined an "amalgam of […] thinking about, historical sleuthing [for relevant facts], and inspired guesswork[.]"(Dennett's italics)

Marcel Kuijsten, a student of Jaynes's and founder of the Julian Jaynes Society wrote in 2006: "To support his theory, Jaynes [drew on] evidence from a wide range of fields, including neuroscience, psychology, archeology, ancient history, and the analysis of ancient texts." For example, Jaynes analyzed 1950's research by Wilder Penfield, who had applied electrical stimulation to patients' brains and produced 'voices', as well as the ground-breaking research by Roger Sperry on the effects of so-called "split-brain" surgery. Jaynes analyzed the history and theory of hypnosis based on his and others' clinical research. He similarly discussed his own and others' studies on the character of psychotic hallucinations, both auditory and visual, that were poorly understood and were typically targeted by psychiatrists for elimination rather than study. Jaynes extensively discussed schizophrenia, covering its complexities, its history as a disease and its relationship to consciousness. Aside from clinical research, Jaynes drew on the accounts of 'gods' recorded in ancient epic poetry, including the Homeric epics and the Akkadian literature from Ancient Mesopotamia, and on the analysis of Ancient Egyptian religion as interpreted by modern scholars, as well as on the accounts of prophecy as described in the Hebrew Bible. He explored the history and psychology of oracles and of spiritual possession as well as music and poetry, in light of the bicameral hypothesis.

Some commentators have noted that the complex arguments for bicamerality are difficult to summarize and explain without "distorting" Jaynes's theory or making it "difficult to take seriously." The broad "scope" of Jaynes's argument, evidence and conclusions has also been a reason for academic caution and reservation of judgement as well as a possible reason for hostility from scientists. Jaynes's use of ancient texts as evidence was another reason for academic caution or skepticism.

Are Jaynes's ideas influential?
The matter of Jaynes's influence is a separate source of controversy signified by the wide range of opinions about Jaynes's theories. Mike Holderness, a freelance popular science writer, asked in 1993 "How many students of cognitive science have read [Jaynes's] deeply unfashionable book under, as it were, the bed covers?" Richard Dawkins in The God Delusion (2006) put it sharply by stating that Jaynes's book "... is either complete rubbish or a work of consummate genius; Nothing in between! Probably the former, but I'm hedging my bets."

Philosophers have been divided in the extreme in their attitude to Jaynes and his ideas. Cavanna et.al. (2007) wrote: "Overall, the attitude of philosophers of mind towards the plausibility of a bicameral mind has been controversial." In 2006, philosopher Jan Sleutels remarked, in a footnote, that: "Jaynes's established repute is now such that the merest association with his views causes suspicion." Sleutels wrote:

"In philosophy [Jaynes] is rarely mentioned and almost never taken seriously. The only notable exception is Daniel Dennett who appreciates Jaynes as a fellow social constructivist with regard to consciousness. Most outspoken in his criticism is Ned Block, who rejects Jaynes's claim as patently absurd."

Ned Block had reviewed Jaynes's book in 1977, writing: "These claims are, of course, preposterous [and] the book contains many confusions . . . juxtaposed in bizarre and stimulating ways . . . to support Jaynes's crackpot claim, but the result is a book that is never boring." Daniel Dennett argued in 1986 that he took "very seriously" what he called "Jaynes' project" while commenting that "as a whole…on the face of it, [the theory] is preposterous, and I have found that in talking with other philosophers my main task is to convince them to take it seriously when they are very reluctant to do this."

The complexity of Jaynes's "multi-disciplinary" theorizing has been offered as a "reason" that his work has been more ignored than tested or refuted. If some have indeed ignored Jaynes, the bicameral hypothesis has nevertheless been described as "undoubtedly influential" by Daniel B. Smith in his 2007 book on "rethinking" auditory hallucinations, where he commented that "... perhaps the only thing that [Jaynes's] boosters and critics agree upon is that [bicamerality] can't be proved." Smith argued that Jaynes's theory matters, whether it is correct or not, because "the problem of voice-hearing is in large part indistinguishable from the problem of consciousness, and that the relationship between the two has been fruitful in determining the attributes of each." Others acknowledged Jaynes's "pioneering work in the field of consciousness studies" and that his bicameral hypothesis has had "widespread influence". Over the years Jaynes's ideas have attracted continuous public attention and occasional academic "reappraisal" or "defense".

The Julian Jaynes Society was founded in 1997, after Jaynes's death, to promote awareness of his work and theories. They maintain a website with a collection of relevant research, and have published collections of essays on related topics.

In 2006, biographers Woodward and Tower reported that Jaynes "felt he had not truly succeeded" in his lifelong work because, in their words, "He was right" about his feeling that "there were people who disagreed with him [who] had not really read his book or understood it." Psycholinguist John Limber concurred, writing "When OC was published, critics had a field day — everyone could find a topic or conjecture that they disagreed with… [Jaynes's ideas were] intriguing, imaginative, preposterous, crazy… In retrospect, most of these critics — myself included — just ignored Jaynes's early chapters [about] what consciousness is not."

Four foundations of the bicameral hypothesis
Four sets of ideas, in the following sequence, inspired and justified the hypothesis of the bicameral mind: 1) consciousness as a product of language; 2) ancient texts indicating an older, non-conscious mentality; 3) the problem of verbal hallucinations; 4) mid-20th-century discoveries about the cerebral hemispheres. (Unless specified otherwise, all quotations in this section are from the original 1976 edition of Julian Jaynes’s book, The Origin of Consciousness in the Breakdown of the Bicameral Mind.)

1. The Jaynesian approach to consciousness
Jaynes introduces the problem of explaining the nature and origin of, by which he means what most people think of as their private 'inner world' of self-reflection, that which is "more myself than anything I can find in a mirror … that is everything, and yet nothing at all[.]" The matter has been problematic for philosophers, psychologists, and biologists since at least the time of Charles Darwin. Most people probably take it for granted that consciousness — the 'inner life' that is linked with ideas of the 'soul' or 'mind' — seems quite familiar, simply 'human nature', "the most self-evident thing imaginable[.]"

For 19th-century psychology, the nature of consciousness was studied in the subjective phenomena traditionally analyzed by introspection, but the methods that introspectionists used were problematic, and were rejected in the early 20th century by behaviorists who sometimes "suggested" that consciousness does not even exist. Jaynes reviews eight solutions proposed since Darwin's time and explains why each failed. He then discusses the various ways that consciousness is not at all what it seems to be. First of all, the term is commonly, and imprecisely, confused with wakefulness or any general "reactivity" of the nervous system (i.e. sensation and perception). For Jaynes, the term is correctly associated with "inwardness", or "what is introspectable", something which seems to be innate and ever-present. However, "consciousness can seem to pervade all mentality when actually it does not." Contrary to commonplace assumptions, 20th-century experimental psychology has shown that consciousness is neither involved with nor even necessary for most behavioral and cognitive processes such as recall of memories, basic learning, problem-solving, decision-making, reasoning and judging. "We have been brought to the conclusion that consciousness is not what we generally think it is. [It] does not make all that much difference to a lot of our activities. If our reasonings have been correct, it is perfectly possible that there could have existed a race of men who spoke, judged, reasoned, solved problems, indeed did most of the things that we do, but who were not conscious at all."

Metaphors
Jaynes observes that the history of trying to understand consciousness is one of "failed metaphors", and the problem resides in the "metaphor language of mind". He explains that metaphors are necessary for people to feel that they understand anything at all. People speak, for example, of the mind as if it were a 'container' or a 'space' inside the head, which of course it is not — except metaphorically; yet it is impossible to speak of the mind or describe it without using metaphors and analogies based on the world of physical behavior. It is impossible even to (i.e. to 'look into' the mind) except metaphorically. Images and ideas do not exist 'in' a mind because a mind and its 'contents' occupy no physical space at all.

Jaynes develops a that explains how metaphors "literally create new objects" such that "language is an organ of perception, not simply a means of communication." It is through language that people "invent mind-space inside our own heads as well as the heads of others," with an invented "structure of consciousness" that echoes "the structure of the world[.]" Jaynes identifies several features of consciousness by which it becomes like a map or model that represents both how a person experiences the world and how the person acts in it, and later functions as the means by which people their world.

"Subjective conscious mind is an analog of what is called the real world. It is built up with a vocabulary or lexical field whose terms are all metaphors or analogs of behavior in the physical world. Its reality is of the same order as mathematics. It allows us to shortcut behavioral processes and arrive at more adequate decisions. Like mathematics, it is an operator rather than a thing or a repository. And it is intimately bound up with volition and decision."

Consciousness is thus "embedded in language"; children learn, through socialization and language acquisition, after they acquire the appropriate conceptual metaphors, to attribute it to others and to themselves. Once learned, it allows people to explain their own and others' behavior in terms of personal agency and responsibility, and it can vary between individuals, across cultures, and over time.

2. Re-reading the Iliad in Homeric Greek
Looking for 'the mind' in ancient literature requires a certain amount of caution. Historically, the learning of consciousness could only have occurred after the origin of language, and the invention of writing happened very late in the history of language, around 3000 BCE. The oldest known written texts are written in hieroglyphics (the "writing of the gods"), hieratic and cuneiform. When those symbols are not explicitly concrete in meaning, their translation requires considerable guesswork. Jaynes asserts that much translation has been done by "modern scholars [who] project their own subjectivity with little awareness of the importance of their distortion."

In searching for evidence of consciousness, the "first writing in human history in a language of which we have enough certainty of translation to consider it […] is the Iliad." This epic poem was set down in writing sometime around 850 BCE but its oldest components derive from around 1230 BCE, the period of the Greek Heroic Age. The mythic account of Greek heroes and gods had been passed down over the centuries by oral tradition, and like all such texts, its newer components mixed new ideas in with the old.

Jaynes's etymological analysis of the 's Homeric Greek reveals that there are "in the older layers . . . no words in the original text for conscious operations, such as think, feel, experience, imagine, remember, regret, etc." The story lacks "mental language"; meanwhile, its human characters engage in "action . . . constant action"; however, ". . . the initiation of action [is] by the gods." (Jaynes's italics) And the gods directly participate in the action as well. Jaynes's re-reading of the Iliad's familiar mythology provides a dramatically succinct description of "the mentality of the Myceneans" that Jaynes calls :

"The preposterous hypothesis we have come to [. . .] is that at one time human nature was split in two, an executive part called a god, and a follower part called a man. Neither part was conscious."

Jaynes asserts that the case for the bicameral hypothesis is "not meant to rest solely on the Iliad[.]" Nevertheless, its oldest content, in Homeric Greek, contains almost nothing to indicate the presence of introspection - but a very different mentality is clearly indicated. The poem, all about action, has a great deal of concrete vocabulary and a nearly total absence of mental vocabulary. All the words "that in a later age come to mean mental things have different meanings, all of them more concrete." For example, psyche is 'blood' or 'breath', but not 'mind'. When the text uses the word soma as the opposite of psyche it never means a living or whole 'body', only 'dead limbs' or 'corpse'. "Perhaps most important is the word noos which, spelled as nous in later Greek, comes to mean conscious mind. It comes from the word noeein, to see. Its proper translation in the Iliad would be something like perception or recognition or field of vision. Zeus 'holds Odysseus in his noos.' He keeps watch over him."

In addition, the characters of the Iliad…

". . . do not sit down and think out what to do. [. . .] The beginnings of action are not in conscious plans, reasons, and motives; they are in the actions and speeches of gods. To another, a man seems to be the cause of his own behavior. But not to the man himself."

The Iliadic gods behaved like humans and were bound by natural laws, but the heroes whose lives they directed were "pushed about like robots[.]" The heroes' world, full of dominating god-figures who speak, and full of feelings acted out without a second thought, "is one of strangeness and heartlessness and emptiness."

Was the Iliad merely a fable and were the 'gods' merely poetic devices? Everyone in the Iliad took the gods for granted, and so did the poet-singers (the aoidoi) who transmitted the epic poem down several centuries; according to tradition, each of the aoidoi chanted the song, with its hypnotically steady rhythms of hexameter verse, as "the entranced bard 'heard' [it]" from his muse. Jaynes acknowledges that the historicity of the Homeric epics is debatable, but for understanding the early history of the human mind he concludes that the Iliad is "a psychological document of immense importance" carrying clues to the historically recent existence of "a very different mentality from our own." And as gods, temples, and mythology were central to pre-classical Greek culture, they were central to contemporaneous non-Greek cultures as well.

3. The character of 'heard voices'
Can the character of Iliadic gods and their speeches be compared to the 'voices' that are today called ? By mid-20th century, the little that was scientifically known about hallucinations had been learned mostly during the medical treatment of psychosis and schizophrenia. Voices have been generally feared as a sign of insanity requiring psychological or neurological treatment, although in some cases they "may be helpful to the healing process"; and they may have been the source of inspiration to "those who have in the past claimed such special selection" as to hear voices of prophecy. Hallucinated 'voices' may be "heard by completely normal people to varying degrees […] often in times of stress [or] on a more continuing basis." Voices occur in all age-groups, come from any location and from every direction, and even "profoundly deaf schizophrenics insisted they had heard some kind of communication." The character of the voices is known to some degree:

"The voices in schizophrenia take any and every relationship to the individual. They converse, threaten, curse, criticize, consult, often in short sentences. They admonish, console, mock, command, or sometimes simply announce everything that's happening. They yell, whine, sneer, and vary from the slightest whisper to a thunderous shout. Often the voices take on some special peculiarity, such as speaking very slowly, scanning, rhyming, or in rhythms, or even in foreign languages. There may be one particular voice, more often a few voices, and occasionally many. [They] are recognized as gods, angels, devils, enemies, or a particular person or relative. Or occasionally they are ascribed to some kind of apparatus reminiscent of the statuary which we will see was important in this regard in bicameral kingdoms."

Medical cases differ in degrees of severity. But why are voices at all "believed, why obeyed"? Because "the voices a patient hears are more real than the doctor's voice." Sound is a modality that cannot be shut out. Voices that have been characterized as command hallucinations cannot be silenced by force of will and if they can be resisted it is only with struggle, even if they command harmful or self-destructive behavior. In less severe cases, some patients "learn to be objective toward them and to attenuate their authority […though at first there is always] unquestioning submission […] to the commands of the voices."

It is normal for healthy, conscious humans to be highly attentive and compliant to 'real' voices of those in recognized authority, especially when the voices are located nearby. For the ancient bicameral human with no conscious self-identity, disobedience to the messages from his or her 'voices' would be literally unthinkable.

". . . if one belonged to a bicameral culture, where the voices were recognized as at the utmost top of the hierarchy, taught you as gods, kings, majesties that owned you, head, heart, and foot, the omniscient, omnipotent voices that could not be categorized as beneath you, how obedient to them the bicameral man!"

Regardless how they are experienced, whether by conscious people today or by bicameral people 4000 years ago, hallucinated voices "must have some innate structure in the nervous system underlying them."

4. The double brain
By the mid-20th century, more was known about the left hemisphere (LH) of the brain than about the right hemisphere (RH), and the LH was called "dominant" because of its seemingly singular responsibility for language. Jaynes accepted the established but rudimentary facts of the day, that language processes are localized in two 'speech areas' (Broca's and Wernicke's) which are normally lateralized to one hemisphere only, but as a research psychologist he was also aware that, if the so-called non-dominant RH had any  functions, they were only beginning to be discovered.. The fifth chapter of Jaynes's book, titled The Double Brain, presented some of the issues and Jaynes's speculations.

Jaynes reported that the usually speechless RH, under certain conditions, can assume some or all the language functions. Thus, a major question that he raised about the normal brain is… ". . . why language function should be represented in only one hemisphere. Most other important functions are bilaterally represented. This redundancy in everything else is a biological advantage to the animal, since, if one side is injured, the other side can compensate. Why then was not language? […] Why was not this without-which-nothing of human culture represented on both hemispheres? [...] Could it be that these silent 'speech' areas on the right hemisphere had some function at an earlier stage in man's history that now they do not have?"

The bicameral hypothesis implies a positive "if tentative" answer, that the evolution of language originally involved both sides of the brain, and that the RH must have had some important function that precluded or restricted its role in normal communicative speech processing: the "language of men was involved with only one hemisphere in order to leave the other free for the language of gods." Jaynes notes and comments on a number of mid-century discoveries about the cerebral hemispheres:


 * 1) Both hemispheres have speech comprehension, but only the left can usually produce speech;
 * 2) Wilder Penfield pioneered in electrically stimulating the brain, sometimes causing patients to hear voices which were experienced, in Jaynes's words, with an "otherness" and "opposition from the self, rather than the self's own actions or own words";
 * 3) Researching the after-effects of the "so-called split-brain operation" to treat epileptics, Joseph Bogen, Roger Sperry, and Michael Gazzaniga found that the two hemispheres could function after surgical separation with apparent independence, creating bizarre behaviors seemingly attributable to "two persons in one head", while in every situation the 'self' of the patient was always identified with the language-dominant hemisphere only;
 * 4) Hemispheric differences of cognitive function at least "echo the differences of god and man." The right-side is better at categorizing and in "synthetic and spatial-constructive tasks while the left hemisphere is more analytic and verbal." "Recognition of both faces and facial expression is […] primarily a right hemisphere function. And to tell friend from non-friend in novel situations was one of the functions of a god."

Jaynes advocates for the newly developing conception of brain plasticity to account for the hypothetical transition of mentality required by his theory:". . . the brain is more capable of being organized by the environment than we have hitherto supposed, and therefore could have undergone such a change as from bicameral to conscious man mostly on the basis of learning and culture. [... The] increasing tide of research has eroded any rigid concept of the brain, [...] the function of brain tissue is not inevitable, and […] perhaps different organizations, given different developmental programs, may be possible.'"

The oldest evidence
The bicameral hypothesis proposes an interpretation of the archeological and historical record that accounts for "the entire pattern of the evidence … in different regions of the world[.]" It connects seemingly disconnected facts and explains apparent mysteries. For example, on the subject of the "Corpse/Personator Ceremony" in early China, Michael Carr wrote:"There are already various non-bicameral explanations for […] all […] Chinese death beliefs and customs. However, without the bicameral hypothesis, at least one explanation has to be proposed for each of them. Proposing many different reasons for corresponding traditions across cultures ignores what Jaynes calls "the entire pattern of the evidence."" The overall pattern of bicamerality, beginning in the 9th millennium BCE and evident in archeology around the world, involves three major "features of ancient civilizations which can only be understood" according to the bicameral hypothesis "wherever and whenever civilization first began":


 * the burial of 'the living dead';


 * the construction and centrality of 'god-houses' (i.e. temples);

Jaynes presents evidence from ancient Sumeria, Ancient Egypt, Ancient Jericho, the Hittites, the Olmec and Maya, and the Inca.
 * the ubiquitous use of idols, statuary and figurines.

The Natufian example
The "best defined and most fully studied Mesolithic culture [is] the Natufian[,]" located at Eynan in present-day Israel. By 9000 BCE they had a population of 200-300 persons living a settled life with primitive agriculture. It was a group too large to be manageable merely by signals and simple commands. The agricultural routines would have been organized by a living leader’s commands at first, and repeatedly heard as needed; later, improvised commands could have originated, as needed, by. The hallucinated 'voices' "heard by the Natufians could with time improvise and 'say' things that the king himself had never said" which is similar to the way that "the 'voices' heard by contemporary schizophrenics 'think' as much and often more than they do[.]"

Natufians practiced ceremonial burials. The dead Natufian king appears to have been propped up in his elaborate tomb-dwelling — "the first such ever found (so far)" —, as if... "...in the hallucinations of his people still giving forth his commands, [... which] was a paradigm of what was to happen in the next eight millennia. The king dead is a living god. The king’s tomb is the god’s house, the beginning of the elaborate god-house or temples[.]" In many places, the first temples were based on this function of the king's tomb as the god's house, and each successor-king was a successor-god. The practice persisted for millennia, as the well-known Egyptian pyramids exemplify. The more common practice, however, was what happened in Mesopotamia, where a successor to an entombed dead king would act as the former king’s priest or servant in the cultic temple where a permanent 'speaking' statue allowed the dead king's speech to still be heard.

Deciphering ancient texts
There have been many "popular books on the subject" of ancient beliefs. All of them are based on applying "modern categories" of human psychology when trying to understand ancient mysterious facts. For scholars too, there is the "enormous and fascinating problem" of interpreting and translating the earliest remnants of the invention of writing. If those records can be deciphered at all, it requires much scholarly guesswork based on facts from other bodies of knowledge. In the case of ancient texts that seemingly deal with abstractions or spiritual or psychological content, scholars who labor to understand them generally begin with the unexamined assumption that human psychology thousands of years ago was fundamentally the same as it is today. Jaynes writes,

"When the terms are concrete, as they usually are, for most of the cuneiform literature is receipts or inventories or offerings to the gods, there is little doubt of the correctness of translation. But as the terms tend to the abstract, and particularly when a psychological interpretation is possible, then we find well-meaning translators imposing modern categories to make their translations comprehensible [... and] to make ancient men seem like us[.]"

Two kinds of theocratic kingdoms
The cultures of ancient Mesopotamia and ancient Egypt are the most studied and best understood of the great cultures of pre-classical antiquity. Their extensive written records from before the Bronze Age collapse have been very successfully translated. The two cultures were quite different from ours today, and from each other as well, but what they had in common was a rigid social hierarchy that bound politics and religion closely together. They were each, in fact, a dominated by ’gods’ and elaborate priesthoods. A survey of the evidence indicates that bicameral kingdoms, which probably began out of similarly primitive bicameral origins, developed in either of two ways:


 * the " [… of the] Mesopotamian bicameral city-states" appeared in some variety as "the most important and widespread form of theocracy [... in] Mycenae[, ...] and, so far as we know, in India, China, and probably Mesoamerica";


 * the "more archaic" system was the " in which the king himself is a god […and] this form existed in Egypt and at least some of the kingdoms of the Andes, and probably the earliest kingdom of Japan."

Mesopotamia
The basic facts of Ancient Mesopotamian religion (or Sumerian religion) are fairly well-established from the archaeology and texts of the Sumerians and Akkadians. Shrines and statues of gods, mostly made of wood, were everywhere, and they were central to daily life. Throughout Mesopotamia, from the earliest times of Sumer and Akkad, all lands were owned by gods and men were their slaves. Of this the cuneiform texts leave no doubt whatsoever. Each city-state had its own principal god, and the king [was] "the tenant farmer of the god." The god himself was a statue. The statue was not a god (as we would say) but the god himself. […] The gods, according to cuneiform texts, liked eating and drinking, music and dancing; they required beds to sleep in and for enjoying sex with other god-statues on connubial visits from time to time; they had to be washed and dressed, and appeased with pleasant odors; they had to be taken out for drives on state occasions; and all these things were done with increasing ceremony and ritual as time went on. Jaynes asks: "How is all this possible, continuing as it did in some form for of years as the central focus of life" if not because of bicamerality?"Everywhere in these texts it is the speech of gods who decide what is to be done. […The] rulers [are] the hallucinated voices of the gods Kadi, Ningirsu and Enlil. [...And] statues underwent mis-pi which means mouth-washing, and the ritual of pit-pi or "opening of the mouth." [...] Each individual, king or serf, had his own personal god [and] lived in the shadow of his personal god, his ili [who was responsible for every action.]"

Egypt
Many basic facts of ancient Egyptian religion are similarly well-established, based on the decipherment of texts in hieratic and Egyptian hieroglyphics (meaning the "writing of the gods"), but many texts have been interpreted according to modern ways of thinking. For example, the creator god Ptah is written about in the Memphite Theology, which… ". . . states that the various gods are variations of Ptah’s voice or 'tongue.' Now when 'tongue' here is translated as something like the 'objectified conceptions of his mind,' as it so often is, this is surely an imposing of modern categories upon the texts."

Commenting on the basic mythology of the pharaohnic god-kings, "that each king at death becomes Osiris, just as each king in life is Horus[,]" Jaynes asserts:

"Osiris [...] was not a 'dying god,' not 'life caught in the spell of death,' or 'a dead god,' as modern interpreters have said. He was the hallucinated voice of a dead king whose admonitions could still […] be heard, [therefore] there is no paradox in the fact that the body from which the voice once came should be mummified, with all the equipment of the tomb providing life's necessities: food, drink, slaves, women, the lot. There was no mysterious power that emanated from him; simply his remembered voice which appeared in hallucination to those who had known him and which could admonish or suggest even as it had before he stopped moving and breathing."

…and the process repeated from generation to generation.

The and
Jaynes agrees with mainstream scholarship that an important but confusing "fundamental notion" in Ancient Egyptian religion is that of the ka. Jaynes observes that… ". . . this particularly disturbing concept, which we find constantly in Egyptian inscriptions, [has been translated] in a litter of ways, as spirit, ghost, double, vital force, nature, luck, destiny, and what have you." Texts about the ka are numerous and confusing. "Every person has his ka[. ...] Yet when one dies, one goes to one's ka." Some texts "casually say that the king has fourteen ka's!" Bicamerally interpreted, the ka is "what the ili or personal god was in Mesopotamia." Usually, the Pharaoh’s ka is depicted as his twin, formed at the time of birth. Bicamerally, Pharaoh heard his ka while alive, while others would hear their own ka and would also hallucinate the Pharoah’s voice as the Pharaoh's ka, which was later still heard by others after Pharaoh’s death.

A related concept is that of the ba, which was usually depicted as a small humanoid bird associated with a corpse or statue of a person. The "famous Papyrus Berlin 3024, which dates about 1900 B.C." records the "Dispute of a man with his Ba", but it has never been translated "at face value, as a dialogue with an auditory hallucination, much like that of a contemporary schizophrenic."

Breakdown of bicamerality
"The smooth working of a bicameral kingdom has to rest on its authoritarian hierarchy." The admonitory functions of hallucination could respond reliably to familiar and non-threatening situations, but would presumably be less reliable in unfamiliar or unmanageable situations. Over the course of many centuries, certain challenges to hallucinatory authority forced it to adapt, or sometimes proved it unable to do so:
 * The success of civilized life added to populations, which meant more individuals' 'voices' needed to be managed in order to maintain social order. Every established bicameral theocracy became polytheistic and had a hierarchy of priests to manage potential competition between the gods of the pantheon; "...such theocracies occasionally did [...] suddenly collapse without any known external cause."


 * The psychological "authority of sound" was gradually weakened, certainly by the mid-2nd millennium BCE, by the widespread use of written texts: being seen by the eye, they could be shut from view and their authority avoided in a way that verbal hallucinations could not.
 * Inter-cultural contact between city-states, also as a result of growth, could either lead to trade relations or to conflict — but nothing in-between — depending on whether the gods on each side judged the as friend or foe. A judgement of the 'other' as hostile could easily lead to war, which certainly brought social chaos.
 * Natural catastrophes, like wars, were disruptive events that likely brought social chaos, followed either by long periods of rebuilding, or by migrations and potentially hostile contacts between individuals and populations.

In the event of serious social disorder, "the gods could not tell you what to do[.]" They became silent, or they produced more disorder. During the 3rd millennium BCE Mesopotamians began the first forms of prayer rituals and sacrificial offerings, probably to invoke 'voices' that were absent in the face of a difficult problem. At a later time, probably in the absence of 'voices', divination rituals and the reading of omens became common practices — not in order to 'tell the future', but to help a king, priest or other inquirer decide what needed to be done. Eventually, and continuing into the 1st millennium BCE, Mesopotamian religion had created a superstitious world filled with countless angels and genii — beneficial half-human, half-bird messengers to the now 'distant' gods — plus countless demons, against whom protection was sought by the widespread use of amulets and exorcisms.

Dating the dawn of consciousness >>>
Jaynes writes of the Assyrian Spring and the limited historical record that might indicate the first acts of consciousness near the end of the 2nd millennium BCE. A thousand years earlier, the city owned by "Ashur" rose to become the trading empire of Old Assyria, then collapsed and rose anew about 1380 BCE, becoming the 2nd Assyrian Empire, a militaristic, brutal conqueror unlike any before it. And the new Assyrians encountered a chaos widespread throughout the region, with migrations of many peoples perhaps fleeing other calamities. Jaynes considers the cause in the catastrophic eruptions of the volcano on the Aegean island of Thera:

Some believe it to have occurred in 1470 B.C. Others have dated the collapse of Thera between 1180 and 1170 B.C. when the whole of the Mediterranean, including Cyprus, the Nile delta, and the coast of Israel, suffered universal calamity of a magnitude that dwarfed the 1470 B.C. destruction. Whenever it was, whether it was one or a series of eruptions, it set off a huge procession of mass migrations and invasions which wrecked the Hittite and Mycenaean empires, [and] threw the world into a dark ages within which came the dawn of consciousness.

The chaos of the period has been described by some historians, writing after Jaynes, as the catastrophic. Natural disaster did not cause a collapse of bicamerality but "certainly accelerated" it. While Jaynes can only approximate the dating and scale of the calamities, he asserts that the recorded unprecedented cruelty of the Assyrian king Tiglath-Pileser I may have been a response to the total collapse of bicameral social control. "The very practice of cruelty as an attempt to rule by fear is, I suggest, at the brink of subjective consciousness."

Of the well-dated books of The Biblical prophets, the oldest is the Book of Amos, written during the 8th century BCE, about the same time as the writing down of the Iliad. The Book of Ecclesiastes dates from about 500 years later. Here are some of Jaynes's comments comparing the two:

""In Amos there are no words for mind or think or feel or understand or anything similar whatever; Amos never ponders anything in his heart; he can't; he would not know what it meant. In the few times he refers to himself, he is abrupt and informative without qualification; he is no prophet, but a mere "gatherer of sycamore fruit"; he does not consciously think before he speaks; in fact, he does not think as we do at all: his thought is done for him. He feels his bicameral voice about to speak and shushes those about him with a "Thus speaks the Lord!" and follows with an angry forceful speech which he probably does not understand himself. Ecclesiastes is the opposite on all these points. He ponders things as deep in the paraphrands of his hypostatic heart as is possible. And who but a very subjective man could say, "Vanity of vanities, all is vanity," (1:2), or say that he sees that wisdom excels folly (2:13). One has to have an analog ‘I’ surveying a mind-space to so see. And the famous third chapter, "To every-thing there is a season, and a time to every purpose under heaven . . ." is precisely the spatialization of time, its spreading out in mind-space, so characteristic of consciousness[...] Ecclesiastes thinks, considers, is constantly comparing one thing and another, and making brilliant metaphors as he does so. Amos uses external divination, Ecclesiastes never. Amos is fiercely righteous, absolutely assured, nobly rude, speaking a blustering god-speech with the unconscious rhetoric of an Achilles or a Hammurabi. Ecclesiastes would be an excellent fireside friend, mellow, kindly, concerned, hesitant, surveying all of life in a way that would have been impossible for Amos.""

Evolutionary speculations >>>
Language: Jaynes outlined his own theory of language evolution that allowed for language in both hemispheres, focusing on the social functions of vocabulary. The earliest humans, in very small groups and with little or no language, must have been organized like other primates, who manage their strict social hierarchies using mostly "postural or visual signals" in accordance with the principles governing primate sociality. The transition to vocal signals may have gone through a series of stages, from vocal signals, to modifiers, then to nouns, and then to the invention of perhaps around 10,000 BCE. The use of names was a necessary step in the evolution of the hallucinatory function as a side-effect of language comprehension, as they enabled the management of larger, settled populations. For preconscious humans — who could not tell themselves what to do — the ability to identify a 'voice' with the leader's name, and to 'hear' the leader when the leader was absent, would have provided evolutionary advantages. Bicameral hallucinations would have enhanced the cohesion of a small group and reinforced the mechanisms of social control that allowed groups to settle and grow in numbers; they enabled better management of non-habitual behaviors that allowed individuals to persist at long-term tasks which were essential for the transition from prehistoric hunter-gatherer societies to agricultural economies. Plasticity: Jaynes also advocated for a concept of plasticity in the child's brain, based on evidence that "under certain conditions"" the normally preferred modes of neural organization" are bypassed,  and he speculated that the modern functional organization of the brain was achieved by 'selective pressure' against bicamerality:  "after a thousand years of psychological reorganization in which [...] bicamerality was discouraged when it appeared in early [childhood] development, [the right hemisphere language] areas function in a different way."

'Voices' from the right hemisphere
Of the four major hypotheses of Jaynes's general psycho-historical theory, his "double brain" neurological model for bicameral voices is the one that is theoretically testable. He allows that his model "could be mistaken (at least in the simplified version I have presented) and the other [hypotheses] true." The model is meant to explain both ancient and modern hallucinations, on the assumption that they are "similar"; their consequences are not identical, however, since conscious people who "relapse" into hallucinations are not bicameral.

"For schizophrenia, whether one illness or many, is in its florid stage practically defined by certain characteristics which we have stated earlier were the salient characteristics of the bicameral mind. [...] But there are great differences as well. If there is any truth to this hypothesis, the relapse is only partial. The learnings that make up a subjective consciousness are powerful and never totally suppressed. And thus the terror and the fury, the agony and the despair. [...T]he florid schizophrenic is in an opposite world to that of the god-owned laborers of Marduk or of the idols of Ur."

The hypothesis attributes bicameral voices to the "amalgams of admonitory experience" — such as remembered commands from parents — that were "stored" in the RH (right hemisphere). The RH would be activated by "decision stress" to send a communication to the LH. Jaynes argues that a linguistic "code" (i.e. a verbal command) would be "the most efficient method of getting complicated cortical processing from one side of the brain to the other." Excitation from the RH is the critical factor, and the most likely short route for a RH message to be transferred to the LH (which holds Wernicke's area) is through the because that is a direct physical connection between the RH and LH temporal lobes.

Jaynes offers two variations of the underlying neurology. The "stronger" variation, supposedly easier to test, is that 'voices' are generated the RH and sent across the anterior commissure to be 'heard' in Wernicke's area. The weaker (and vaguer) model would still have excitation originate in the RH, but the "articulatory qualities of the hallucination" would somehow involve the normal LH location for speech-production, i.e. Broca's area.

Authoritarian character of the bicameral mind
For thousands of years before the 2nd millennium BCE, bicameral societies were authoritarian — but there was no oppression:"...the bicameral mind was the social control, not fear or repression or even law. There were no private ambitions, no private grudges, no private frustrations, no private anything, since bicameral men had no internal ‘space’ in which to be private, and no analog 'I' to be private with. All initiative was in the voices of gods. And the gods needed to be assisted by their divinely dictated laws only in the late federations of states in the second millennium B.C.   Within each bicameral state, therefore, the people were probably more peaceful and friendly than in any civilization since."

Because of the bicameral neurological processes, the psychology of ancient humans was characterized by obedience to a voice (or voices) whose commands were necessary for many life activities, all of which happened without introspection or self-reflection. The 'voices' would have sounded as real as any external voice. They were "admonitory voices" echoing a parent's or chief's voice of authority that had previously been heard and stored in the right hemisphere as "admonitory experiences". When they commanded action, they did so with absolute authority because, in the absence of reflective consciousness, the person "could not 'see' what to do by himself" and simply acted according to instructions.

The authoritative, commanding voices from the right hemisphere of the brain's non-conscious decision-making processes. In other words, the bicameral voices expressed the individual's non-conscious which was wholly obedient to, and shaped by, the social order. When a bicameral person faced a problem "that needed a new decision or a more complicated solution than habit could provide, [the resulting] decision stress was sufficient to instigate an auditory hallucination." When a right-hemisphere voice 'spoke', it was a product of the person's own (unconscious) 'thinking' which, as long as the communal order was stable, was always consistent with the social hierarchy and cultural system of the group.

Bicameral instabilities
Bicameral societies changed slowly over the millennia, but some changes, for example inter-cultural contact and trade, periods of expansive population growth, and natural calamities probably weakened the effectiveness of the bicamerally hallucinated divine beings. While inherent instabilities made many bicameral theocratic kingdoms susceptible to collapse, only in the later millennia, after recurring breakdowns of bicameral authority, was the adaptive behavioral response of consciousness possible; it eventually did occur, probably at different times and places.

The effects of writing
Human language evolved with deep roots in the hearing of sounds, by the use of ears that cannot be closed and cannot turn away. The invention of writing, which relied on the visible form, made language into something in a fixed location that could be seen by eyes, or not, because the eyes can turn away or be shut. Thus the use of writing was one factor that contributed to the eventual decline of the authority of sound, and so of bicamerality. Originally, however, early texts were probably written on behalf of, and read by, the 'gods' of the right hemisphere, and the person looking at the text perhaps got the message more as "a matter of  […], that is, hallucinating the speech from looking at [written] picture-symbols[.]" In Mesopotamia, the use of writing to encode 'divine law' (that is, the "judgement-giving") that was told to Hammurabi by his god (either Marduk or Shamash) probably enhanced the social order, at least at first. The practice of recording god-commanded events possibly helped the gods (i.e. the right hemisphere) remember and learn from their own past. The constant bicameral recitations and repetitions of such texts eventually produced culturally-defining epic poetry, which was also a bicameral process. By the 1st millenium BCE, however, the bicameral texts remained as cultural artifacts, and the narratization process gave way to a major characteristic of consciousness, namely the individual's "ability to narratize memories into patterns[.]"

A visual component >>>
>>> auditory hallucinations were often accompanied by visions...

The General Bicameral Paradigm >>>
To explain many of the mysterious psychological phenomena associated with "diminished consciousness" in the modern world, Jaynes proposed a hypothetical structure he called the General Bicameral Paradigm. The paradigm has four aspects:
 * the, or belief system, a culturally agreed-on expectancy or prescription which defines the particular form of a phenomenon and the roles to be acted out within that form;
 * an or formally ritualized procedure whose function is the narrowing of consciousness by focusing attention on a small range of preoccupations;
 * the itself, a response to both the preceding, characterized by a lessening of consciousness or its loss, the diminishing of the analog 'I,' or its loss, resulting in a role that is accepted, tolerated, or encouraged by the group; and
 * the to which the trance is directed or related to, usually a god, but sometimes a person who is accepted by the individual and his culture as an authority over the individual, and who by the collective cognitive imperative is prescribed to be responsible for controlling the trance state.

The GBP has been applied to various phenomena to demonstrate how they are vestiges of ancient bicamerality. Some were known in his time to have significant right hemisphere involvement, others are recognizable as displaying bicameral characteristics. Jaynes's book offers, for example, a theory of oracles and sibyls; an analysis of how prophecy and possession are similar yet significantly different; an analysis of music, poetry and song; hypnosis as a trance phenomenon.

Criticisms and rejoinders
Jaynes is quoted in 1978 describing the wide range of academic responses to his book as “from people who feel [the ideas are] very important all the way to very strong hostility.” Academic debate over Jaynes’s ideas has focused mostly on his notions of consciousness and only indirectly on the bicameral hypothesis. One of the early and persistent critics was philosopher Ned Block who responded harshly to Jaynes’s speculative approach and “preposterous” conclusions. In a short book review in 1977, Block dismissed the notion of a non-conscious mentality as “absurd”. He described Jaynes's book as “strange, fascinating” but “never boring”, containing “many confusions”, “crackpot” and “implausible”. Block’s critique has been described as reflecting “an issue many scientists remain sympathetic to — how could anyone think consciousness is a cultural construction?”

The bicameral mind was not a 'split-brain'
A criticism has been made that "Jaynes' bicameral model requires" that the human brain was split at the time the was written and that, for consciousness to have arisen, "Jaynes believed that the development of nerve fibres connecting the two hemispheres gradually integrated brain function." This argument concludes that "Jaynes's thesis does not stand up to" the fact that there were no recent "radical structural changes in the brain."

This criticism is contradicted by a claim from the Julian Jaynes Society website: "" [original italics] In Jaynes's book, a chapter titled 'The Double Brain' presented discoveries and speculations about between the cerebral hemispheres, at no time suggesting either that they had ever been physically 'disconnected' or that their functions had been 'integrated' by evolution. Jaynes wrote about "the brain's plasticity" in reference to "psychological capacities" and "psychological reorganization", not in reference to "brain architecture" as some critics have stated. Jaynes and his supporters fully agree with the scientific consensus against a physiological disconnection between the two hemispheres:""According to Jaynes, there is no substantial difference between our brains today and those of bicameral people 3,000 years ago.""

The 'use-mention' debate
Philosopher Ned Block argued that Jaynes had confused the "nature of people's thought processes with the nature of their theories of their thought processes." In other words, according to Block, ancient humans could 'use' consciousness but did not 'mention' it in their texts only because they had not developed the of consciousness, yet they, like us, were "surely" conscious because "it is a basic biological feature of us" and also "...it is obvious that [consciousness] is not a cultural construction." In Block's view, Jaynes's ancient evidence can demonstrate nothing about the absence of consciousness, only that "the concept of consciousness arrived around late in the 2nd millennium B.C."

Daniel Dennett (who, like Jaynes, held that consciousness is a cultural construction) countered that there are, such as money, baseball, and consciousness, that cannot exist without the  of the thing. Jaynes acknowledged Dennett's argument, adding that "...there are many instances of mention and use being identical." The concepts, e.g. of money, or law, or good and evil, are the same as the thing. Rather than 'confusing' the concept of consciousness with the use of it, Jaynes replied, "we are fusing them [because] they are the same."

Is the bicameral hypothesis science or theology?
Sociologist W. T. Jones, whose primary interest was the "sociology of belief", asked in 1979 "Why, despite its implausibility, is [Jaynes's] book taken seriously by thoughtful and intelligent people?" Jones conceded — in agreement with Jaynes — "that the language in which talk about consciousness is conducted is metaphorical" but he flatly contradicted the idea, as Jones put it, "that consciousness 'is' metaphorical or that it has been 'created' by metaphor"; rather, in Jones's view, a metaphor is simply a "verbal token . . . that 'stands for' [an] experienced similarity[.]" Jones also argued that Jaynes was "biased" with respect to three "cosmological orientations": 1) that Jaynes showed "hostility to Darwin" and to gradualist natural selection; 2) that Jaynes had both "a bias against consciousness" and a "longing for 'lost bicamerality'" and believed (says Jones) that "we would all be better off if 'everyone' were once again schizophrenic"; 3) that Jaynes had a "desire for a sweeping, all-inclusive formula that explains everything that has happened[.]" Jones stated that "those who share these biases [...] are likely to find the book convincing; those who do not will reject [Jaynes's] arguments." Jones dismissed the bicameral proposition by calling it "secular theology" and by denying that it was scientific, and he even questioned whether Jaynes intended to be taken seriously. He described Jaynes's book as:

"... not a scientific treatise at all - not scientific history nor scientific archaeology nor scientific neurophysiology. And if that is the case, then it should not be judged by the usual criterian [sic] for assessing scientific hypothesis. [. . . I]t presents a vision of the world as a whole [...] in a language that looks scientific, rather than in the language of theology. [...] My description of Mr. Jaynes’ book as secular theology [explains] the reasons for [the book’s] success, despite its lack of scientific rigor[;. . .] that it is a new gospel, a world-picture startlingly different from any we are accustomed to and one in which everything has its secure place and all is accounted for."

Jones was described, in 1993, by Laura Mooneyham White as "one of Jaynes's most thoroughgoing critics[.]" White interpreted Jones’s critique as part of a debate between the values of scientific and non-scientific ways of knowing, between "scientific and visionary discourse". According to White, Jones and many other scientists rejected the notion of a "radical discontinuity" dividing human beings from other biological forms; therefore they rejected Jaynes’s argument that consciousness marked such a discontinuity. White interpreted Jaynes as affirming discontinuity when, in 1983, he said: "I am a strict behaviorist [only] up to 1000 B.C. when consciousness develops in the one species that has a syntactic language, namely, ourselves." White commented: "This belief in discontinuity, in an absolute break between conscious human beings and other forms of life, has garnered Jaynes an inordinate amount of criticism from his fellow scientists, as one might expect." The discontinuity Jaynes "tolerates" is not metaphysical, however, but exists "in terms of natural science alone": the divide between bicamerality and consciousness is a consequence of "complex social relationships" and language; Jaynes rejects a metaphysical explanation for both religion and consciousness. White argued that "... for Jaynes, all forms of questing after transcendence are […] equally compelling, equally misguided. The religious imperative [inherited from bicamerality] is inescapable but doomed as chimerical." Jaynes, however, applies this critique not only to religion but to science as well, because the search for truth through science is a modern "quest for authorization" and for "certainty" in the wake of lost bicamerality. Jaynes wonders aloud about what motivates science:

"In this final chapter, I wish to turn to science itself and point out that it too, and even my entire essay, can be read as a response to the breakdown of the bicameral mind. For what is the nature of this blessing of certainty that science so devoutly demands in its very Jacob-like wrestling with nature? Why should we demand that the universe make itself clear to us? Why do we care?"

Jaynes "identifies Darwinism, Marxism, Freudianism, and behaviorism" as major examples of "scientisms" of the modern era:

"[those] clusters of scientific ideas which come together and almost surprise themselves into creeds of belief, scientific mythologies which fill the very felt void left by the divorce of science and religion in our time."

Near the end of his book Jaynes says of it, twice, "this essay is no exception." According to White, Jones "seized upon [this admission] as crucial evidence of the unscientific nature of Jaynes’s ideas." But White concluded that Jones's position may have come from a rival scientism that cannot allow discontinuities, and cannot recognize its own dependence on "the necessary relationship between any comprehensive scientific theory and [a system of] belief."

On Jaynesian distinctions
Psycholinguist John Limber wrote in 2006, that “... most [early critics of Jaynes] — myself included — just ignored Jaynes’s early chapters [about] what consciousness is not.”

In 1990 Jaynes acknowledged that his whole argument was "contradictory to the usual and . . . superficial views of consciousness," and he reiterated that "the most common error" people make "is to confuse consciousness with perception." "But there can be no progress in the science of consciousness until careful distinctions have been made between what is introspectable and all the hosts of other neural abilities we have come to call cognition. Consciousness is not the same as cognition and should be sharply distinguished from it."

The 'Self' is something put together as a product of consciousness over a "lifetime" of experiences and stories, something that "we come to construct or invent, on a continuing basis, in ourselves and in others" as "the answer to the question 'Who am I?'" The Jaynesian view differs from the "classic notion of 'mind' or self" as "an individually bounded, embodied, efficient cause," a view which is to some extent expressed, on the one hand, in the neuroscience reductionism that sees consciousness as a 'neurological event', and on the other hand in the cognitive science model that sees it as a 'mental state'. The 'Self' of Jaynesian consciousness is not the brain in whole or in part, nor an event in the brain, and not a state of the brain.

Whether consciousness is confused with perception or not, its role in volition or 'self-control' is often presumed. In his book, Jaynes explains how it is that thinking happens before consciousness of thinking: "one does one's thinking before one knows what one is to think about." (Jaynes's italics) Jaynes made a definitive statement about volition, but about its bicameral, non-conscious form: "The explanation of volition in subjective conscious men is still a profound problem that has not reached any satisfactory solution. But in bicameral men, ... volition came as a voice that was in the nature of a neurological command, in which the command and the action were not separated, in which to hear was to obey."

The problem of volition is also related to another fundamental feature of consciousness, namely "narratization", which is tied to the notion of the 'Self', while its role in volition is limited. Jaynes argued that it possibly originated in the non-conscious, right-hemisphere function of "narratization in epics" by which the bicameral 'gods' organized memory of their own "god-commanded events". With consciousness, it was changed into a "story-telling" that put memories and experiences into sensible patterns. Oakley and Halligan, the authors of a 2017 paper, echo Jaynes's distinction between consciousness and volition in their discussion of the "personal narrative". They describe "the non-consciously generated, self-referential psychological content of the personal narrative" as a major aspect of consciousness, and they argue that the "contents of consciousness" are products of "executive self-control" systems that operate outside "conscious experience":

"Despite the compelling subjective experience of executive self-control, we argue that “consciousness” contains no top-down control processes and that "consciousness" involves no executive, causal, or controlling relationship with any of the familiar psychological processes conventionally attributed to it."

Ancient mirrors and the 'mirror test'
In 1990, Jaynes discussed and rejected certain claims that the is evidence of self-awareness in animals. The 'Self' which is constructed in Jaynesian consciousness is not the body or the face: what a person or an animal sees in a mirror is not the 'Self'.

"Self-awareness usually means the consciousness of our own persona over time, a sense of who we are, our hopes and fears, as we daydream about ourselves in relation to others. We do not see our conscious selves in mirrors, even though that image may become the emblem of the self in many cases. [...] The animal [looking in a mirror] is not shown to be imagining himself anywhere else, or thinking of his life over time, or introspecting in any sense — all signs of a conscious self."

Jaynes asks whether the use of mirrors in antiquity is evidence of ancient consciousness, and he alludes to research, new at the time, examining the "mystery" of Mayan mirrors that were possibly used for divination.

On 'zombies' and other 'fringe minds'
Since the 1990's, much philosophical discussion about consciousness has inconclusively revolved around the notion of the "philosophical zombie" — an imaginary entity human-like in all respects except that it lacks 'consciousness' or 'experience' of some sort which the philosophers variously refer to with terms like "subjective character of experience" or "qualia" or "phenomenal consciousness". These terms and concepts, which Peter M. Hacker has sharply critiqued, are largely unconnected to Jaynes's arguments. Even so, some philosophers have rejected the possibility of bicamerality because it seems 'zombie-like' "based on definition of consciousness, not Jaynes's." (author's italics) Bicameral humans were not 'philosophical zombies': "While the ancients surely were aware and had perceptual experiences like ours, is it possible they did not have the interior dialogue that Jaynes refers to? Like other readers, I had projected my own pre-existing notion of consciousness onto OC, neglecting Jaynes's own words..."

"Bicameral man was intelligent, had language, was highly social, and could think and problem-solve; only these processes took place in the absence of an introspectable internal mind-space."

Jan Sleutels and Gary Williams have attempted to clarify the differences between, on the one hand, the 'concepts' and 'thoughts' usually associated with conventional notions of consciousness, and on the other hand, the less familiar 'nonconscious concepts' necessary to make sense of bicamerality and Jaynesian consciousness. Sleutels discusses how the problematic nature of bicameral humans (i.e."Greek zombies") is precisely a problem of how to understand the "fringe minds" of creatures such as "infants, early hominids, animals" that cannot speak about their 'minds'. Williams has argued for "three forms of mentality (reactive, bicameral, J-conscious)" as a way to reconcile the philosophers' terminology within a Jaynesian framework.

Relevant Research
One early study, in 1982, had results that suggested some support for Jaynes’s model. A paper in the American Journal of Psychiatry in 1986 argued against it. A decade later, new neuroimaging techniques were used in a study that was discussed in The Lancet and in the Journal of Psychiatry and Neuroscience in support of Jaynes’s theory. Much remains to be learned about how the hemispheres differ and how they communicate with each other in the normally connected, healthy brain. Since the 1960's, the study of so-called "split brains", caused by surgically "cutting the corpus callosum," has been a major source of knowledge about the abilities of each hemisphere and the differences between them.

The 'split-brain': one mind or two?
In a 2020 paper on split-brain research, the authors state that "the central question, whether each hemisphere supports an independent conscious agent, is not settled yet" and there is still no definitive answer to "the intriguing question of how unity of consciousness is related to brain processes." In this paper the problem of the 'unity of consciousness' does not distinguish between 'introspection' and sensory, especially visual, awareness. The paper asserts that, to date, more is known about visual processes than about other cognitive abilities, perhaps because of "a bias throughout cognitive neuroscience and psychology, leading to a strong focus on vision in split-brain research." In addition, the prevailing view among cognitive neuroscientists is "that consciousness [visual awareness] in a split-brain is split" because of the assumption that "each cortical hemisphere houses an independent conscious agent." The "currently dominant theories about conscious awareness - the Integrated Information Theory [...]and the Global Neuronal Workspace Theory [...] - may be critically dependent on the validity of this [split consciousness] view."

Contrary evidence is discussed. For example: in some split-brain patients "perceptual processing is largely split, yet response selection and action control appear to be unified under certain conditions." This indicates that some sort of inter-hemispheric communication takes place despite the 'split', so that the 'independence' of the hemispheres cannot be clearly established.

The paper suggests for future research that the "first question" to be answered towards the goal of "understanding unity of mind" is to improve understanding of RH language abilities.

Phenomenology of 'voices'
The term, which implies all kinds of 'sound-like' phenomena, is often used specifically for "voices" (as in the quotations below), which are the most common cases and are more precisely called AVH (auditory verbal hallucination). The of verbal hallucinations have been minimally researched:"Auditory hallucinations — or voices — are a common feature of many psychiatric disorders and are also experienced by individuals with no psychiatric history. Understanding of the variation in subjective experiences of hallucination is central to psychiatry, yet systematic empirical research on the phenomenology of auditory hallucinations remains scarce."

A 'voice' is not always 'auditory': sometimes, with non-verbal or "fuzzy" hallucinations "a message or meaning is communicated without being heard (soundless voices)."

Most research into hallucinations has been done to learn how better to be rid of them, since most studies have been done with patients for whom the 'voices' are distressing:"Auditory hallucinations (AVH) have been described since antiquity, but have been identified as pathological only for the last 3 centuries. [...] AVH are characterized by the perception of voices without external stimuli, typically located outside of themselves by patients but also, and more and more described, from within of [sic] the subject’s head. The content of voices is frequently accompanied by a negative emotional valence and often with a lived experience described as distressing. [...] The pathophysiology underlying AVH is far from fully understood. [...] In summary, morphological and functional studies of AVH primarily report modifications in the temporal cortex, making this brain area a potential target for brain stimulation to reduce AVH.""

Some recent studies have looked at comparisons between the AVH of psychotics and those of healthy 'hearers'. Those cases associated with are particularly relevant for the bicameral hypothesis:"Command hallucinations are widely regarded as distressing and indicative of high risk of harm to self and others [and] might be the dominant experience for individuals with a schizophrenia diagnosis[.]"

The of AVH is a matter of importance because the various "sub-types" may have different causes.

Hemispheric asymmetries and plasticity
Anatomical hemispheric asymmetries, which are found in many species, are thought to correlate with evolutionary advantages for "lateralized specialization" of functions, and in humans particularly with language and handedness. These correlations are interrelated in complex ways by genetics, neuro-chemistry, embryonic events, experience and disease. Some asymmetries, or some degrees of asymmetry, may depend less on genetics than on brain plasticity in response to developmental and experiential events: for example, some aspects of lateralization might be decided by fetal positioning in the womb, or fetal exposure to ultrasound. While chimpanzees and humans might have some hemisphere asymmetries in common, the greater degree of asymmetry in the human brain seems generally indicative of higher human abilities such as language.

While both sides "resemble" each other at the "macrostructural" level, they differ developmentally, and the hemispheres may mature into varied "types" of hemispheric functional organization. Functional and cognitive consequences of anatomical asymmetries require further study, and recent research has focused on comparing variability of 'normal' and 'atypical' cerebral asymmetry, and different cognitive processes can lateralize in different ways, accounting for "reversed asymmetries or the absence of asymmetry" as well.

One major difference is that "the left hemisphere has a greater preference for within-hemisphere interactions, whereas the right hemisphere has interactions that are more strongly bilateral."

Right-hemisphere language
The "era of the classical model" of locations and LH (left hemisphere) exclusivity for language "is over." The "essential" RH role in language is becoming increasingly appreciated.

"The right hemisphere is critical for perceiving sarcasm, integrating context required for understanding metaphor, inference, and humour, as well as recognizing and expressing affective or emotional prosody–changes in pitch, rhythm, rate, and loudness that convey emotions."

In their 2005 paper, Mitchell and Crow present an extensive review of essential RH "higher order language functions" and dysfunctions, followed by their "four-chambered" neuro-psychological theory of language that emphasizes the "right hemisphere language functions [necessary] for successful social communication[.]"

While exploration of RH language abilities has mostly been done in the context of recovery from lost LH abilities, studies have more recently looked at the normal RH role in language processing among healthy, conscious people, as well as language deficits from RH damage. Such research of normal, "essential" RH language abilities is necessary to better understand the neuropsychology of language in general, but also that of schizophrenia.

Cerebral torque and bi-hemispheric language
The most prominent aspect of asymmetry in the human brain, known since at least the 1980's, is the counter-clockwise twist, or "cerebral torque" which has also been called the "Yakovlevian torque". A 2019 systematic analysis of cerebral torque concluded that it is a specifically human, genetically-defined, 3-dimensional pattern underlying "the uniqueness of asymmetries in the human brain." A uniquely human evolutionary event might account for the torque and its developmental progression in the human embryo, where the RH starts with an earlier and more advanced structural growth of the "" parts of the cortex, and the LH follows later, with structural enhancement in the parts of the LH cortex.

In 2005, Mitchell and Crow interpreted the effect of cerebral torque as a challenge to the simplistic view of LH dominance for language. They "...outline a bi-hemispheric theory of the neural basis of language that emphasizes the role of the sapiens-specific cerebral torque in determining the four-chambered nature of the human brain in relation to the origins of language and the symptoms of schizophrenia."

In their model, not only would language functions be quite different each hemisphere, but, because of the torque, there might be two asymmetric channels for inter-hemispheric language processing — primarily R to L across the "anterio-motor" lobes (near Broca's area), primarily L to R across the "posterio-sensory" lobes (near Wernicke's area). The LH internally is primarily responsible for sensory-motor processing and primary lexicon, while the RH, with "a degree of autonomy" stores "a second part of the lexicon, comprising more remote, variable and often affectively charged associations"; processing the RH "gives rise to distinction between meanings on the one hand [posteriorly], and thoughts and intentions on the other [anteriorly]."

Bi-hemispheric models
An explosion of discoveries and speculations about brain laterality have taken place since Jaynes began his writing on the matter in the 1960's. In 1990, he expressed caution against "popularization" about the 'two sides of the brain' that verged on "shrill excesses" of interpretation. Still, he felt that research findings to that time were "generally in agreement with what we might expect to find in the right hemisphere on the basis of the bicameral hypothesis."

In 2005, Marcel Kuijsten (founder of the Julian Jaynes Society) reviewed research that "provides strong evidence for Jaynes's neurological model" while acknowledging that the "neurobiology of hallucinations is complex and a definitive theory has not yet emerged." Kuijsten claimed in 2016: "Beginning in 1999, numerous neuroimaging studies have demonstrated a right/left temporal lobe interaction during auditory hallucinations, confirming Jaynes's neurological model." The Society maintains a website with supporting research.

Also in 2005, Mitchell and Crow presented their "bi-hemispheric theory of the neural basis of language" that explicitly addresses the problem of 'voices'. Their "four-quadrant concept...provides a framework for understanding the phenomena of psychosis" because, in their view, "schizophrenia and language have a common [evolutionary] origin". The authors refer to Jaynes and then present their model of how "auditory hallucinations [could] arise in the right hemisphere, and perhaps for that reason lack the characteristic of being self-generated."

Unresolved issues
A study in 2010 concluded that "decreased language lateralization" (i.e. greater than normal RH language activity) is characteristic of psychotics with AVH (auditory verbal hallucinations), but the researchers could not establish that the same was true for AVH-hearers in general. Just as there are sub-types of AVH experience, there might be multiple mechanisms to account for them.

Cases of AVH with more negative experiences, such as command hallucinations, seem to be more strongly connected to "reduced leftward asymmetry", and in general, "the relative lack of asymmetry observed in schizophrenic brains" correlates with "disrupted inter-hemispheric connectivity" or with greater than normal RH activity. How the corpus callosum regulates inter-hemispheric communication remains uncertain.

A paper in 2019 reported that "current literature emphasizes a concept that AVH result from abnormal activation, connectivity and integration within the auditory, language, and memory brain networks." Looking at connectivity among the "interhemispheric auditory pathways" the authors built on "a steadily growing number of studies using a variety of [neuroimaging] modalities" plus "clinical, cognitive and cellular level" studies to present "converging evidence for an interhemispheric miscommunication due to [excitatory-to-inhibitory] imbalance as one correlate of AVH[.]"

Alternate models
LH inner speech: An alternative psychological approach to AVH emphasizes the study of normal "inner speech" — when people 'talk to themselves' — and how it can sometimes be abnormally experienced or mis-interpreted as an alien voice, i.e. as an auditory hallucination. It is unclear how the 'motor' act would be converted into a 'perceptual experience'.

LH speech perception error: A LH "inner hearing" (rather than 'inner speech') model has been proposed, suggesting that "auditory hallucinations generate activity in the speech regions in the left hemisphere much like real auditory input (causing a perceptual experience)."

Traumatic memory: Traumatic or abusive experiences have been suggested as the source of the "strongly negative emotional component" of hallucinations, but "only about 10-20% of the 'voices' patients experience 'hearing' is about actual memories[.]"