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NewVERS.12 1Mar24. The hypothesis of the bicameral ("two-chambered") mind is about the neurological basis of verbal hallucinations and their cultural importance, especially in ancient history. It asserts that hallucinated voices are caused by the brain's two-sided structure, and that 'voice-hearing'  once dominated human psychology, made the first civilizations possible, and was the naturalistic cause of early supernatural concepts and religions. The hypothesis is part of a far-reaching psycho-historical theory proposed by research psychologist Julian Jaynes in his 1976 book, The Origin of Consciousness in the Breakdown of the Bicameral Mind, where Jaynes argues that consciousness correctly understood is something "learned and not innate", that it first occurred late in the 2nd millennium BCE, and that everyone in the preceding millennia had a “mentality based on verbal hallucinations" that was in some ways similar to schizophrenia in the modern world. Jaynes called it a  because psychologically it had two parts, one dominating the other but "...neither part was conscious." Evidence is drawn from linguistics, ancient texts, archaeology, behavioral and comparative psychology, and clinical studies of schizophrenia and the so-called "split brain". Part of the argument is that ancient humans had sensations and language, and lived mostly habitually just as people do today, but they left no cultural evidence of any 'inner self' or 'conscious mind' because they had none, that is, they had not learned to introspect on their own actions and experiences. Instead, the ancient records are conspicuously about people 'hearing' one or more 'voices of authority' that commanded action, could not be disobeyed, and ruled over daily life. Such "voices of chiefs, rulers or the gods" were often associated with natural phenomena or hand-made 'divine' images. In terms of the hypothesis, this preconscious 'bicamerality' arose because the biological evolution of language involved both cerebral hemispheres (not just the left as per mainstream neurolinguistics), such that the left hemisphere would 'hear' the right hemisphere 'speak' as though it were a separate, dominant being.

The hypothesis potentially explains many "otherwise mysterious facts" of ancient history such as idolatry, polytheism and oracles. Also many modern phenomena with varying degrees of trance or "diminished consciousness", such as hypnosis and severe schizophrenia, might be explainable as "vestiges" of ancient bicamerality when the brain supposedly worked in a "more primitive" way than today. The hypothesis has influenced modern research into hallucinations in the general population and today voice-hearing is not always judged as mental illness. Groups such as the Hearing Voices Movement seek meaning in the experience which is known to be reported in most, possibly all, cultures, often with a spiritual significance. Alternative hypotheses about voice-hearing, or auditory verbal hallucinations, have been proposed, but as of 2020, the phenomenon remains poorly understood both neurologically and historically.

Jaynes's overall theory, of an evolved bicamerality and of a later, learned consciousness, has been promoted as a "revolutionary idea" and a "new scientific paradigm" that challenges common assumptions about human nature, mental health and religion. One early reviewer called it "ingenious [and] remarkable [... yet] exasperating [in its] incompleteness". Based on "bold" interpretations of the known facts, the theory has been described as largely unproveable. About Jaynes's approach to consciousness, one early critic rejected it as "absurd", another as "biased" against evolution. Supporters, while acknowledging that "Jaynes’s work is generally dismissed" or has been mostly "ignored" by many experts, contend nevertheless (as of 2016) that Jaynes’s theorizing is "ahead of much of the current thinking in consciousness studies" and that "critiques of the theory are [mostly] based on misconceptions about what Jaynes actually said".

Jaynesian psycho-historical theory
The bicameral hypothesis was one of several components in a "large" psycho-historical theory "covering so much of the terrain of human nature and history". The theory came to public attention in 1977 in The Origin of Consciousness in the Breakdown of the Bicameral Mind, a book by Julian Jaynes (1920-1997), a respected lecturer and research psychologist at Princeton University from 1964 to 1995. The book, his one and only, was written for general readers on the results of "his lifelong work" on the problem of consciousness. The bicameral hypothesis, about the nature and importance of verbal hallucinations in early civilizations, emerged in the context of Jaynes's contention "that a civilization without consciousness is possible".

Background: the problem
Early in the 1800's psychology was called "the science of consciousness" and by century's end introspection was not only the main method of study but almost a synonym for. This "traditional view defines consciousness as the direct awareness or immediate experience of the contents and processes of mind [and the] method of observing consciousness, so defined, is introspection". During the 20th century the traditional view was early on ignored by many in favor of behaviorism then later on consciousness was defined as awareness and was so studied through brain research. Although the traditional view had been widely abandoned, its problems had not been resolved. One psychologist in 2006 rephrased the traditional problem as, "Just what is it that makes a brain seemingly "introspectable?""

The 'nature' of consciousness
Jaynes saw the problem of consciousness in traditional terms, affirming that its "denotative definition is, as it was for Descartes, Locke, and Hume, what is introspectable", one's 'innermost sense of self' and completely distinct from perception. Introspection is something like observation, but without a sensory organ, and whatever the 'mind's-eye' 'sees' is perhaps something 'mental', but is certainly not the internal reality. Jaynes argued that introspection is an 'inner sense', and the 'inner space' or 'inner world' of consciousness "must be a metaphor of real space." Jaynes wrote that "Subjective conscious mind is an analog of what is called the real world", something like a map that is 'built', first, "through metaphorical language" and then 'operates' (metaphorically) through linguistic or visual metaphors and analogies. His main claims include: that most of the time people act habitually without consciousness, since it is irrelevant for most behavior but can help to "shortcut behavioral processes and arrive at more adequate decisions"; that "there is no operation in consciousness that did not occur in behavior first"; that consciousness is not a state or process of neurology but a way of using language; it is "learned and not innate"; and is therefore created by culture rather than evolution. Consciousness has several distinct features (e.g. mind-space and narratization) which can vary between cultures, and children can learn these at a late stage of language acquisition, but only through socialization. Jaynes's view was influential with later social constructivist theorists such as Daniel Dennett.

Consciousness in history
Jaynes also hypothesized that consciousness had, late in the 2nd millenium BCE. On his analysis, there is no clear evidence of interiority or introspection before that era. He argued that consciousness was a cultural "invention" like agriculture and writing, a "new mentality" that became possible "only after the breakdown" of an older, mentality and cultural system. The breakdown of the older mentality was not a specific, one-time event, but a gradual process stretched over centuries. Certain processes of language change were involved in the historical origin of consciousness, and other social processes allowed it to spread across cultures or be learned by children.

Bicamerality
Jaynes further hypothesized that before the ancient origin of consciousness, human mentality was in fact hallucinatory, with a divided psychology caused by the way language evolved in the brain, which according to Jaynes must have occurred in both cerebral hemispheres. He came to call it a (i.e. "two-chambered") mind as "...a rather inexact metaphor to a bicameral legislature of an upper and lower house." The idea of a "preconscious mentality", one that was, moreover, based on verbal hallucinations, was so extraordinary that, in anticipation of readers' reactions, Jaynes himself introduced it (with obvious irony) as "preposterous". Nevertheless, the bicameral hypothesis was intended to explain, as scientifically as possible, a wide range of important facts of the early history of civilizations and religions.

The transition from bicamerality toward consciousness is considered an on-going historical process affecting all of human culture. The continuing legacy of the bicameral mentality is evident mainly in religious traditions with ancient roots, but also in a variety of persistent forms of "diminished consciousness" which might all share a common genetic and neurological basis in the two-hemisphere structure of the human brain. Since the middle of the 1st millenium BCE, consciousness has flourished and interacted with "the rest of cognition" to expand human abilities and accelerate cultural change.

Implications and significance
The bicameral hypothesis touches a "staggering" range of subjects, and has many "far-reaching" implications:
 * the evolution of language involved both sides of the brain, and the organization of language in the brain is changeable;
 * the first verbal hallucinations might have been "a side effect of language comprehension which evolved by natural selection as a method of behavioral control" for early small groups;


 * the bicameral system of social control and organization enabled the first agricultural civilizations wherever they arose;


 * bicamerality can explain "our first ideas of gods" as evident in the polytheism, idolatry, and theocracy of ancient societies worldwide;
 * the "weakening" of bicameral 'voices', in part by the invention of writing, can explain the 2nd millennium BCE beliefs in demons and angels which served as "hybrid human-animal" intermediaries to the gods; these supernatural beings were later supplemented by spiritualistic and magical practices, such as divination, incantation of spells, amulets, prayers, and oracles, etc., all aimed at invoking, appeasing or replacing the increasingly absent or unreliable gods;
 * the inherent instabilities of bicamerality might explain both the slow pace of growth during the early millennia of civilized society, as well as the rapid social breakdown of the 'Bronze age collapse';
 * in the modern world, many phenomena 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". They comprise "a large class of phenomena of diminished consciousness", or some degree of trance, and only some are hallucinatory, yet all might be "vestiges of the bicameral mind". Examples of possible vestigiality are: music and poetry; prophecy, spiritual possession, and glossolalia; hypnosis; schizophrenia; shamanism; and "the 'invisible playmates' of childhood; [...] and hundreds more."

In the final chapter of Jaynes’s book he philosophically interpreted the long cultural transition from bicamerality. Jaynes wonders, "Why should we demand that the universe make itself clear to us? Why do we care?" Noting that "the urgency behind mankind’s yearning for divine certainties" is recorded as the "drama . . . of the central intellectual tendency of world history", he argues that all modern religious, pseudo-religious and superstitious systems, including "faith in various pseudosciences", spring from the same psychological discomforts felt when bicameral voices were originally lost.

Modern science can also exhibit "the same quasi-religious gestures" and generate "scientisms [... or] scientific mythologies which fill the very felt void left by the divorce of science and religion in our time." The historical "secularization of science" expresses the "erosion of the religious view of man [that has been and] is still a part of the breakdown of the bicameral mind." For Jaynes, religion exists and persists not for metaphysical reasons but because it is rooted in the brain. 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." Consciousness, by contrast, is given a but also  origin that marks a "radical discontinuity" between humans and the rest of nature. The "archaic authorization" for civilized action originally came from voice-hearing that controlled behavior, but having broken down, it would to a great degree be replaced by selfhood, self-control and moral responsibility. As Jaynes put it:"[V]oices 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."Yet such a 'self' is psychologically suggestible and can be displaced, often in trance-like, obedient service to a 'higher power' (e.g. a hypnotist, demagogue, 'demon', or voice): Jaynes proposed a to explain this social process that often "allows a more absolute control over behavior than is possible with consciousness."

Reception and influence
Jaynes's arguments and conclusions were called "ingenious" and "remarkable", yet also "exasperating" and "incomplete". Some early commentators noted that the arguments for bicamerality are difficult to summarize and explain without "distorting" Jaynes's theory or making it "difficult to take seriously."

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 that Jaynes 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)

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 and the possibility that humanity experienced an historic change of mentality, 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.

The broad "scope" of Jaynes's argument, evidence and conclusions has been one 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.

The complexity of Jaynes's "multi-disciplinary" theorizing has been seen as a "reason" that his work has been more ignored than tested or refuted. One commentator noted that among early critics of Jaynes’s proposals, "everyone could find a topic or conjecture that they disagreed with". 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." 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." Philosopher Jan Sleutels in 2006 argued in support of plausibility, but noted that "Jaynes's established repute is now such that the merest association with his views causes suspicion" and commented:"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."

From an atheist viewpoint, Richard Dawkins in 2006 considered Jaynes's arguments and described his book as "either complete rubbish or a work of consummate genius, nothing in between! Probably the former, but I'm hedging my bets. [...] Whether or not you find his thesis plausible, Jaynes's book is intriguing enough to earn its mention in a book on religion."

Over the years Jaynes's ideas have attracted continuous public attention and occasional academic "reappraisal" or "defense". Researchers have acknowledged that Jaynes was a pioneer in the modern study of consciousness and that his bicameral hypothesis has had "widespread influence", especially regarding the idea of separate roles for each cerebral hemisphere. The hypothesis "inspired much of the modern research into hallucinations in the normal population [since] the early 1980s" and today voice-hearing is not always judged as mental illness. Groups such as the Hearing Voices Movement seek meaning in the experience which has ancient forms such as "the prophetic phenomenon" of Biblical Israel and is known to be reported in most, possibly all, cultures, often with religious or spiritual significance.

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. Its founder, Marcel Kuijsten argued in 2016 that Jaynes’s theorizing "continues to be ahead of much of the current thinking in consciousness studies", "remains the most supportable and generalizable explanation for the occurrence of auditory hallucinations, and provides voice-hearers with a historical context to better understand their experience." Kuijsten contends that "the vast majority of critiques of the theory are based on misconceptions about what Jaynes actually said".

Argument and evidence
The bicameral hypothesis, that there once was a mentality different from consciousness and it was all about 'gods' who were hallucinations, is an inference from "multiple independent sources of evidence" which can be interpreted in many ways.

The possibility of a preconscious mentality
The Jaynesian idea, that humans could, and at one time did, live without consciousness (i.e. introspection, or "interiority"), is not easy to understand or explain.

Introspection, which for Jaynes is the sole basis of any "conception of what consciousness is," identifies "a succession of different conditions which I have been taught to call thoughts, images, memories, interior dialogues, regrets, wishes, resolves, all interweaving with the constantly changing pageant of exterior sensations of which I am selectively aware." Such are the 'contents' of recalling, reminiscing or reflecting on experience and behavior, or imagining past and future possibilities. All these, however, are "a much smaller part of our mental life than we are conscious of, because we cannot be conscious of what we are not conscious of[...]!" Behaviorism and experimental psychology in the 20th century have shown that much of human activity, like that of other animals, involves physiological processes that are mostly automatic and habitual. One can acquire scientific knowledge that such neural and cognitive processes exist and 'be conscious' of them when 'reflecting' on them, even though they cannot be experienced.

Jaynes criticized "superficial views of consciousness that are embedded both in popular belief and in language" which treat it as 'all of mentality' or as "that vaguest of terms, experience"; or they fail to distinguish "between what is introspectable and all the hosts of other neural abilities we have come to call cognition" including processes of awareness (which he called "reactivity"), attention, perception, and automatic learning, problem-solving or decision-making which all happen either without any experience of the process, or before any consciousness of the result. Not only is consciousness far less of mentality than is commonly supposed, it is neither a constant nor necessary condition for most behavior; nevertheless our "consciousness of consciousness" to provide knowledge of what is called one's 'inner self' and one's own 'conscious mind'.

It was the idea of — of the mind as a 'space' filled with 'mental entities' or 'mental events' — that Jaynes defined as the "primary feature" among several that comprise the "basic connotative definition of consciousness." When people speak about private thoughts, or 'mental life', it is simply a part of what it means to be conscious to speak as if there is a "mind-space inside our own heads as well as the heads of others". The 'mental activities' that supposedly occur 'in the mind', like all human physical activities, certainly involve the brain, but nobody has direct experience of their brain at work, and introspection can never reveal how the brain works (i.e. nerve impulses, synapses, etc.). Phrases like the 'inner world' or 'mind's eye' of introspection refer to the mind and its 'contents', not the brain; however,, as Jaynes puts it: "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 generally through the use of metaphors that people feel that they anything at all, and he develops an original theory of metaphor to explain how the assumed mind-space and other features of consciousness operate. By assuming and speaking of the existence of a 'mind', 'soul', 'inner world' or 'inner self', people learn to act and to explain everyone's behavior as if caused or controlled by something 'on the inside'.

Furthermore, if consciousness is based on linguistic metaphors and analogs, then it can only be a human ability, and can emerge only at a certain level of linguistic and social complexity. Therefore, says Jaynes, consciousness cannot be innate, and is a product of language and culture, not biological evolution. And if it is not a necessary part of human psychology, then 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 oldest 'mind words'
Jaynes notes that if the earliest remnants of the invention of writing can be deciphered at all, correct translation requires much scholarly guesswork based on facts from other bodies of knowledge. He argues that the standard approach of translators is to apply modern psychological ideas when trying to understand ancient mysterious facts, a method which naively assumes 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[.]" The presence of consciousness in the past can only be inferred, and only when certain words are in a context referring to the existence or acts of a person’s 'inner' being. Contrary to ordinary assumptions, Jaynes argues that no words for 'the mind' as we understand it today are found at all in the oldest texts, especially those that are well-understood, such as Greek and Hebrew.

Example: The
The, an epic poem based on oral traditions from the 12th century BCE, was written down about 400 years later, and may be "the earliest writing […] in a language that [modern readers] can really comprehend". Jaynes analyzes this well-studied source of Greek mythology, and makes the case that the oldest parts, in Homeric Greek, tell nothing of an 'inner life', which allows the possibility that at one time it did not exist. In Jaynes's words:"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." Bruno Snell made a similar point: "...there is in Homer no genuine reflexion, no dialogue of the soul with itself." This contrasts with late classical Greek literature of the middle 1st millennium BCE. Jaynes emphasizes that the Greek words are originally, in the, always concrete, referring to limbs, organs or bodily actions; Jaynes analyzes key terms, including , (also )…  and discusses as well how they eventually transformed into mental words.

The 'gods' preceded 'mind'
Without the use of mental vocabulary, the explicitly depicts its human heroes as being stirred into action by ‘gods’, and they explain their own behavior as caused by gods who themselves take part in the action. The humans never "sit down and think out what to do". Jaynes considers that these interactions between 'gods' and ordinary humans are similar to modern hallucinations, which are reported as 'voices', most often by people diagnosed with psychosis.

This "suggests" an entirely new psychological interpretation of the 'mythological' content of the and its epic poetry form: that the Homeric gods were not simply imaginative poetic devices, and Greek society before the 5th century BCE took the gods seriously; furthermore, that in the late Bronze Age and for centuries into the early Iron Age, those who recited or heard the heroic tales accepted the reality of the gods because people commonly experienced god-voices in their own hallucinatory way. The becomes for Jaynes "a psychological document of immense importance",  providing one ancient clue to the hallucinatory mentality that he calls the "bicameral mind".

Modern hallucinated voices
Based partly on his own clinical work and research, Jaynes argues that by the mid-20th century, the little that was scientifically known about verbal hallucinations had been learned mostly during the medical treatment of psychosis and schizophrenia. He recognizes that 'voices' have been generally feared as a sign of insanity requiring 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 experience is varied and complex: "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." 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, and sound is a modality that cannot be shut out. Hallucinated voices 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 (as so-called command hallucinations often do). 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."

Language and the cerebral hemispheres
If the ‘hearing of voices’ has any physiological basis at all, then it has something to do with the way language is organized in the brain. Jaynes acknowledges and reviews the known facts of his day showing that language is essentially a function of one cerebral hemisphere, most commonly the left. He asks why this should be so, and why "those areas on the right hemisphere corresponding to the speech areas of the left" should seem to have “no easily observable major function”, yet can, under certain conditions, take over partial or full language functions. Jaynes speculates about the evolution of "their important function, [.]"(original italics)

Research by Wilder Penfield from the 1950's showed that 'voices' could be 'heard' by patients when the right cerebral cortex was electrically stimulated.

Ground-breaking 1960s studies of the so-called "split brain" showed that the two hemispheres can behave with a great deal of apparent independence, and while the right hemisphere can understand language, only the left (dominant) hemisphere seems to be associated with a person's self-identity.

Jaynes incorporates such evidence to support the “tentative” possibility that verbal hallucinations generally come from the language areas of the right cerebral hemisphere and, if so, would sound to the left hemisphere as if spoken by another being.

Bicameral mind and bicameral society
The existence and character of the ancient system are "demonstrated in the literature and artifacts of antiquity." The bicameral mind is describable, however, only by comparison to modern consciousness and especially modern hallucinations, about which too little is known. Other than what people say of their experience, there is no explicit, objective method to verify the existence or character of hallucinations that seem externally real, just as the same is true of an 'inner life' of consciousness.

A divine mentality
"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. This is almost incomprehensible to us. And since we are conscious, [we] wish to understand[.]"

"In distinction to our own subjective conscious minds, we can call the mentality of the Myceneans [and their era] a . Volition, planning, initiative is organized with no consciousness whatever and then 'told' to the individual in his familiar language, sometimes with the visual aura of a familiar friend or authority figure or 'god', or sometimes as a voice alone. The individual obeyed these hallucinated voices because he could not 'see' what to do by himself."

"For this [hypothesis], the evidence is overwhelming. Wherever we look in antiquity, there is some kind of evidence that supports it [...] Apart from this theory, why are there gods? Why religions? Why does all ancient literature seem to be about gods and usually heard from gods?"

The hallucinatory roots of civilization
"The bicameral mind is ... that form of social control which allowed mankind to move from small hunter-gatherer groups to large agricultural communities. [It] evolved as a final stage of the evolution of language [in which] lies the origin of civilization."

Human group-life and language evolved together. Pre-historic groups were small, their patterns of behavior were simple, and they "moved through their lives on the basis of habit — just as we do" today. While language was simple and vocabulary was still too concrete for consciousness, the ancients "knew what followed what and where they were, and had behavioral expectancies and sensory recognitions just as all mammals do". While routine behaviors would have been manageable by the vocal commands of a living parent or leader, repeatedly given as needed, social cohesion would be enhanced by the ability to recall the leader's commands.

The first hallucinated 'voices' may have been echoes of real vocal signals that evolved along with language comprehension to allow long-term behavioral control. Larger groups, however, required more than the simple hallucinated memory of a leader's commands: the 'voices' "could with time improvise and 'say' things that the king himself had never said", just as "the 'voices' heard by contemporary schizophrenics 'think' as much and often more than they do[.]"

Before about 9000 BCE "voices would have played a minor role" but provided the "system of social control" that enabled the more complex life of settlements and agriculture in the first civilizations. This was the case in the oldest civilizations until about 1000 BCE, after which voices became a "hindrance". Such was the case also in different parts of the world and in younger civilizations where the "advance to consciousness occurred quite late" (as perhaps occurred among the Incas after "their conquest by Pizarro").

Social control by 'voices'
Although modern, and presumably ancient, hallucinated voices occur within the individual's brain, they usually sound as 'real' and external as any human voice, and are often more authoritative. Jaynes claimed about schizophrenia that:

"... 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."

Hallucinations are thus dependent on cultural context as well as neurology. This applies to modern voice-hearers (who live in a world of consciousness) and especially to schizophrenic patients who struggle with "hallucinations that are unacceptable and denied as unreal" by others. Bicameral people, however, lacked consciousness and 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 modern idea that such voices 'came from their own heads'.

The archaeological record of the most well-understood early civilized societies and kingdoms, when they were stable, presents a rigid hierarchic structure, with divine beings at the top; the bicameral interpretation is that everybody relied on voices of authority, whether they were from a real person or a hallucinated divinity, that told the individual what to do. Civilized life, which Jaynes described as "the art of living in towns of such size that everyone does not know everyone else", required bicameral authoritarianism, but he argued it was not oppressive:"...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."

Experiencing bicameral voices
In the modern world, occasions of learned conscious thinking are normal events in the context of otherwise habitual life; when hallucinations occur, they are often "triggered by stressful, confusing, or "fight or flight" situations." In bicameral times, when habitual, repetitive activities presumably dominated life, the threshold for psychological stress was probably much lower than today. Any decision-making situation, where "a change in behavior was necessary because of some novelty", or where a problem was somewhat too complicated for normal habits, "was probably sufficient" to trigger a voice.

Bicameral decision-making, an entirely unconscious process, was based on a lifetime of "admonitory experiences", i.e. being told by others what to do. A bicameral voice did not reason or 'think out loud' (as conscious people do) to solve a problem or make a decision. The 'voice' simply conveyed the result of non-concious, automatic processes of the nervous system in the form of a message or command. Today, the of similar processes are sometimes evident in the content of a person's consciousness, while consciousness is falsely deemed to be the source of the decision. In bicamerality, the habitual conditioning by accumulated experiences and the general social order could generate an admonitory 'voice'.

When the ancient individual heard a voice speaking a command, the command was authoritative and could not be disobeyed because it expressed the brain's unconscious volition. However, at no time could a 'voice' be described or dismissed as 'one's own': for the bicameral human with no mind-space or conscious self-identity, there was no ability to judge the wisdom of the received messages, and disobedience would be literally unthinkable. Jaynes wrote: ". . . 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!"

A visual component
Besides the stress of decision-making, certain sounds, such as wind and waves, might have had hallucinogenic effects in bicameral times, and so too could many visual stimuli, such as awe-inspiring vistas, clouds, sea mists, strange lighting and shadows, drawings, carved images, and ritual objects including stone idols. Visual hallucinations are less commonly reported than auditory, but when they occur with voices, usually "they are merely shining light or cloudy fog", and they often have "flitting and bird-like movements."

The Jaynesian "double brain" model of hallucinations
In the 1990 edition of his book, Jaynes specified that his psycho-historical theory consists of four "separable" hypotheses. They are: the nature of consciousness; the dating of the 'dawn of consciousness'; the existence and character of the preconscious bicameral mind; and the proposed neurological model for hallucinations. Of the four hypotheses, his "double brain" neurological model for 'voices' is the one that is theoretically testable, but Jaynes knew "it would be decades before...his ideas could be tested."

The neurological model underlying the bicameral mind was inspired by mid-20th-century discoveries about the cerebral hemispheres. The important and surprising facts included that both sides could comprehend language while only the left controlled speech, and that 'voices' could be 'heard' by electrical stimulation of the right hemisphere's cerebral cortex. So-called "split brain" studies, especially, were not only demonstrating the conditional independence of the hemispheres, but were also generating much popular and scientific discussion about altered and complementary "modes of consciousness" (e.g. propositional/appositional, verbal/visuospatial, analytic/holistic) that were possibly related to the duality of the cerebral hemispheres.

Jaynes assumed that modern language functions are normally localized and lateralized in the left hemisphere, but he hypothesized that archaic processes of language communication between the hemispheres could provide a neurological explanation to support his bicameral hypothesis.

Bicameral and non-bicameral hallucinations
Jaynes's neurological model is meant to explain ancient hallucinations primarily, on the assumption that they are similar but not identical to modern hallucinations since conscious people who "relapse" into hallucinations are not bicameral. About schizophrenia, Jaynes wrote: "... 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."

Jaynes allowed that his neurological model "could be mistaken (at least in the simplified version I have presented) and the other [hypotheses] true." The model attributes voices, especially in the ancient bicameral mind, 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 proposed two variants of his neurological model. The "stronger" variation, supposedly easier to test, is that 'voices' are generated entirely the RH to be 'heard' in Wernicke's (LH) 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.

Evolutionary speculations
Language: Jaynes outlined his own theory of language evolution to account for language in both hemispheres and to focus on the social functions of vocabulary. The earliest humans, with little or no language, lived in very small groups which must have been organized to manage their strict social hierarchies, like those of other primates, using mostly "postural or visual signals" in accordance with the principles governing primate sociality. Vocabulary may have grown through a series of stages, from vocal signals, to modifiers, then to nouns, and then to the invention of perhaps around 10,000 BCE. Names enabled the management of individuals within larger, settled populations. The evolution of names was a necessary step towards the hallucinatory function, which was a side-effect of language comprehension.

For preconscious humans — they could not tell themselves what to do — the ability to 'hear' the leader when the leader was absent, and to identify the 'voice' with the leader's name, would have provided evolutionary advantages. Bicameral voice-hearing would have enhanced the cohesion of a small group and reinforced the mechanisms of social control over larger populations, enabling individuals to persist at the long-term tasks which were essential for the transition from prehistoric hunter-gatherer societies to agricultural economies. Brain 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."

The pattern of evidence
The bicameral hypothesis permits an interpretation of archeological and historical facts that accounts for the general pattern, says Jaynes, of "social organization [...] wherever and whenever civilization first began" and specifically "the entire pattern of the evidence [of] the dead as gods in different regions of the world". The hypothesis 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.""

Early bicamerality
There are "several outstanding archeological features of ancient civilizations which can only be understood", says Jaynes, according to the bicameral hypothesis. They include the burial of "the important dead as if they still lived"; the ubiquitous use of idols, statuary and figurines; the monumental architecture, especially of 'god-houses' (i.e. temples) "in which no one lived, no grain was stored, and no animals were housed". Jaynes presents evidence from ancient Sumeria, Ancient Egypt, Ancient Jericho, the Hittites, the Olmec, Maya, and the Inca. The living dead. The hallucinated 'voice' of a group leader would still be 'heard' after the leader's death, and so the leader could seem, at least for a time, as still giving commands. Such an experience can explain the origin, as early as 9000 BCE, of certain ceremonial treatments of the dead as still living. One was burial beneath the home (as at Tel Jericho) or at the dwelling entrance (as at the "Pre-Pottery Neolithic B site of Tel Halula"). Another was the practice by Paleolithic skull cults of severing the head from a corpse and preserving the skull (as at Göbekli Tepe). In many places there was a "double burial of the same corpse", perhaps because the 'voices' had stopped being heard. Elaborate mummification rituals, practised for thousands of years and in widely separated parts of the world, were aimed at preserving a physical body, perhaps to satisfy the 'afterlife' demands of a still-heard voice. In later millennia, texts refer to the dead persisting as "ghosts" if not "as gods". 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. They may have been a bicameral community. 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[.]"

Statuary. A prominent feature of nearly all early settlements was a place of some kind for cultic statuary. It was not uncommon for a shrine to be located in a personal dwelling (e.g. 7th-6th millennium Çatal Hüyük). Some of the most common and oldest artifacts are strangely formed figurines, statues and cultic images, and thousands of them are small enough to hold in the hand. Many such figurines may have served as hallucinogenic devices that stimulated the 'hearing' of bicameral voices. Monumental god-houses. The burial mounds found around the world were pre-cursors, in many places, of "tremendous architectural investment" in the construction of complex tombs such as the ancient pyramid. Many such tombs for the 'living dead' served as the center of communal life where the "god-king's" presence was long-lasting, if not eternal. The first temples were possibly based on the function of a king's tomb as a "god-house". Alternatively, many large settlements and cities, for example 7th millennium Tel Jericho, or the later ziggurats of Ur, had a centrally located temple that housed a 'speaking' statue-god or life-sized effigy who could rule for multiple generations and in many places at once. Such was probably the case in Mesopotamia, where the cultic statues were maintained for generations by a dead king's successors acting as a servant priest of the statue-god.

Theocratic kingdoms
Of the great cultures of pre-classical antiquity, ancient Mesopotamia and ancient Egypt are the two most studied and best understood. 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 functioned for millennia and that bound politics and religion tightly together. They were each, in fact, a dominated by ’gods’ in an elaborate polytheistic system with a correspondingly elaborate priesthood. The two systems were typical of two types of ancient kingdoms, which probably began out of similarly primitive bicameral origins but developed differently:


 * 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 " in which the king himself is a god" [is the "more archaic" system that] "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 successful decipherment of Egyptian texts in hieratic and hieroglyphics (meaning the "writing of the gods"). Egyptian beliefs and concepts are often stated in concrete terms, and Jaynes stresses that such straight-forward texts are often mis-interpreted and mis-translated to suit modern ways of thinking and philosophizing. For example, Jaynes refers to the creator god Ptah written about in the Memphite Theology, and comments: ". . . 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."

Concerning the central 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: ". . . 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." The Pharaoh and his ka, usually depicted as twins, are formed together at birth. Some texts, however, "casually say that the king has fourteen ka's!" Bicamerally interpreted, the ka is "what the ili or personal god was in Mesopotamia." 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 could still be heard for some time 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." and records the "Dispute of a man with his Ba", has never been translated "at face value, as a dialogue with an auditory hallucination, much like that of a contemporary schizophrenic."

Systemic social breakdown
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 social control by the 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, did the adaptive behavioral response of consciousness become possible; it eventually did occur, probably at different times and places.

Effects of writing
Human language and 'voices' evolved in connection to an auditory system in which the ears, unlike the eyes, cannot be closed; the hearing of sounds cannot be 'shut out'. The invention of writing, which relied on a visual system, connected language to a visual sign in a fixed location that could be looked at or avoided. 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, visual symbols 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 recitations and repetitions of such texts possibly produced culturally-defining epic poetry as a bicameral process. In the 1st millenium BCE, however, while the ancient texts remained as cultural artifacts, the bicameral recitation process eventually gave way to something different, supporting a major characteristic of consciousness, namely the individual's "ability to narratize memories into patterns[.]"

Loss of social order
"The smooth working of a bicameral kingdom has to rest on its authoritarian hierarchy." The admonitory functions of hallucination could respond to familiar and non-threatening situations, but might fail in unfamiliar or unmanageable situations. The success of civilized life increased the numbers of individuals' 'voices' that 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, i.e. the 'voices', of the pantheon. Many "such theocracies occasionally did [...] suddenly collapse without any known external cause." Even the relatively stable bicameralities, such as in Egypt, never resolved polytheistic inconsistencies. Over the course of many centuries, failures of hallucinatory authority required adaptation, or proved to be insurmountable:


 * The psychological "authority of sound" was gradually weakened, certainly by the mid-2nd millennium BCE, by the widespread use of written texts.
 * 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.
 * Besides war, natural catastrophes likely brought social chaos, followed either by long periods of rebuilding, or by migrations and potentially hostile contacts between individuals and populations.

Substitutes for divine authority
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 ancient Mesopotamian religion began to express the first forms of prayer rituals and sacrificial offerings, probably to invoke 'voices' that did not speak automatically in the face of a difficult problem. Before consciousness could "narratize" (i.e. to 'tell the future') about an action and its consequences, a wide variety of divination rituals and the reading of omens became common practices 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.

The dawn of consciousness
The limited historical record of the late Bronze Age currently offers no more than clues to the possible dawn of consciousness. By the end of the 3rd millennium BCE, the city owned by "Ashur" had risen to become a trading empire, Old Assyria. It collapsed but rose anew about 1380 BCE, becoming the 2nd Assyrian Empire, a militaristic, brutal conqueror unlike any before it. The new Assyrians encountered a chaos widespread throughout the region, with migrations of many peoples perhaps fleeing natural calamities. Jaynes asserted that the recorded unprecedented cruelty of the Assyrian king Tiglath-Pileser I may have been a chaotic response to the total collapse of bicameral social order. "The very practice of cruelty as an attempt to rule by fear is, I suggest, at the brink of subjective consciousness."

Natural disasters "certainly accelerated" the collapse of bicamerality. Jaynes originally speculated that the major cause of collapse was a volcanic eruption: Whenever it was, whether it was one or a series of eruptions, [the collapse of Thera] 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.

By 1990, Jaynes deemphasized the volcano as an immediate cause of the "dark ages" because new evidence indicated that the Minoan eruption may have occurred, or begun, as early as 1600 BCE. Even so, some historians writing after Jaynes have described the end of the millennium as the catastrophic 'Late Bronze Age collapse'. It was "a form of systems collapse [. . .that] requires a widespread internal fragility" and a "broad instability" for it to make sense, and Jaynes's theory has been described as possibly the best way to explain it.

Richard Dawkins and Oliver Sacks have claimed that for Jaynes consciousness began when bicameral voices became 'internalized' as one's own. Jaynes, however, does not say that hallucinated voices were 'heard' differently because of consciousness, but that consciousness became possible only after 'voices' were generally silent:""[Before the breakdown of bicamerality in Mesopotamia] the gods customarily had locations...such as ziggurats or household shrines [or] celestial bodies [and] the majority of gods were earth-dwellers along with men. All this changes as we enter the first millennium B.C., when, as we are proposing, the gods' voices are no longer heard.""

Early centuries of transition to consciousness
Jaynes's interpretation of the first centuries of transition to consciousness focused primarily on the ample evidence from the ancient Middle East. Later scholarship aimed at the "tracking of ancient mentalities" elsewhere as well. Certain mysterious Chinese funerary practices can be explained according to the bicameral hypothesis, with the later Zhou dynasty interpretable as a period of “transition” to consciousness from a period "approximately the same as in Greece".

Greece
In Greece, the old order, dominated by (hallucinated) gods, gave way after the so-called 'Greek Dark Age' to a society of newly-conscious humans struggling, philosophically, to the world and their place in it next to the gods. The era has independently been interpreted by some historians as particularly significant without any reference to the bicameral hypothesis, for example Bruno Snell argued that it was the era of the Greek "Discovery of Mind". Karl Jaspers proposed that the early 1st millennium BCE was a global "axial age" of cultural advancement. The widely recognized and well-documented revival of culture known as classical Greece is, for Jaynes, the outcome of a cultural transition away from bicamerality. He described it as the period "when so much of what we regard as modern psychology and personality was being formed for the first time." Individuals, sometimes alone in response to social disorder, or through encountering conscious others, were beginning to learn conscious behaviors. The ability took hold and spread, quickly in some places, slowly in others, while the religious legacy of bicameral culture could adapt only gradually, and began to be seen as irrational.

Hebrew Bible
Regarding the "birth pangs of our subjective consciousness[,]" Jaynes asserts of the Hebrew Bible that "[n]o other literature has recorded this absolutely important event at such length or with such fullness." The scriptures of Judaism combine very ancient traditions together with legends and historical events. The later books of the canon record events between the ninth and fifth centuries BCE, a chaotic period of political and religious conflict reflecting the "mental struggle that followed the breakdown of the bicameral mind." Jaynes devotes a chapter of his book to relevant Biblical themes, including the divine names ( and ), the problems of inconsistent 'voices' both within and between the many prophets ("nabiim" in Hebrew), and the divination practices and ever-present idols mentioned in the texts.

The "prophetic phenomenon" has been described as "universal" across cultures, and "[p]rophets, as individuals and as groups, appear in the earliest stages of Israel's history." Numerous Biblical passages discuss the "pre-classical prophets" of the ninth century BCE, traveling in groups of hundreds throughout the land, with peculiar attire, engaged in a "primary task" of "the delivery of oracles." They "were regarded with some ambivalence...respected and feared [...but could also] evoke contempt [...and] were perhaps despised." Jaynes mentions several episodes from the same period that indicate the elimination of frenzied false prophets he describes as 'groups of bicameral men'.

Much of the physical evidence of idols has been lost, because "King Josiah had them all destroyed in 641 B.C. (II Chronicles 34: 3-7[)]." Jaynes discusses six sorts of idols mentioned in the Hebrew including what he calls the "most common hallucinogenic idol", the that figure in several texts. In the Book of Ezekiel, 21:21 the king of Babylon used divination and consulted with idols who "could seem to speak".

Regarding the 'true' prophets, that they heard a 'voice' was taken for granted. The falsity of others' prophecy varied: either "they prophesied by Baal" (spoke in the name of a 'false god') or "they proclaim visions of their own minds, not from the mouth of the Lord".

Comparing Amos and Ecclesiastes
Of the Biblical books, the Book of Amos is the oldest of those verifiably well-dated by modern scholars. It was written during the 8th century BCE, early in the almost 300-year era of "the classical prophets", at about the same time that the Iliad was first written down among the Greeks. The Book of Ecclesiastes dates from about 500 years later. Jaynes regards these two books as "extremes" of difference that typify comparisons between older, more bicameral, texts and newer, more conscious, texts. Jaynes comments:

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. [...] he does not consciously think before he speaks; [...] 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 [deeply]. 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). [...] Ecclesiastes thinks, considers, is constantly comparing one thing and another, and making brilliant metaphors as he does so. Amos uses external divination, Ecclesiastes never.

Irrationality in classical antiquity
Classical texts reveal attitudes of conscious people towards phenomena that the hypothesis explains as early vestiges of lost bicamerality. For example, Socrates, famous as a rational philosopher, had his "daimonion" (personal deity). As the culture of philosophy and rationality took hold in classical Greece and Rome, religious ecstasy was early on valued as the "divine gift" of madness, while the highest poetry was the form composed "in a state of frenzy". 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 prophets ("nabiim") of the Hebrew Bible have been analyzed by numerous modern scholars as having a psychology of "frenzy" and "ecstasy", if not "psychosis", but according to Abraham Heschel, the rabbis of the Talmud in the post-Biblical era, who viewed all claims of prophecy with suspicion, 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. [... as stated] 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 "famous nabiim", the 'true' prophets who always knew what their 'voices' said, as "men who can be partly subjective and yet still hear the bicameral voice." They differed from the 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 [vestigial] phenomenon is known as possession."

A similar account applies to the sibyls. According to Jaynes's historical analysis the Greek "Age of Oracles" went through six stages as society transitioned from bicamerality to consciousness. Their original simple function, to inspire 'voices', degenerated 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 conscious people.

Vestiges of bicamerality in the modern world
Many phenomena, some familiar and some strange, display varying degrees of "diminished consciousness" or trance. Jaynes argued that such possible "vestiges" of ancient bicamerality are highly dependent on social processes, may possibly involve significant differences in how the cerebral hemispheres interact, with probably significant right hemisphere processing. Jaynes's book included chapters on the following key examples: hypnosis, which is highly dependent on 'outside' authority; a comparison of prophetic voice-hearing and spiritual possession (possible right hemisphere takeover of normally left hemisphere functions); some psychological aspects of music, poetry and song, which all have ancient roots and links to religion. Jaynes also proposed a bicameral historical theory of oracles and sibyls, and argued that the hallucinations of severe schizophrenia might be a "partial relapse" to bicamerality where the subjective consciousness of the "modern schizophrenic struggles against the more primitive mental organization...in which the hallucination ought to do the controlling."

The is a hypothetical social-neurological process proposed by Jaynes to explain certain phenomena (e.g. hypnosis, spirit possession) as vestiges of ancient bicamerality because the bicameral-like functions of the brain might become activated or even dominant. In general, the result is a trance state of diminished consciousness, where the Self, the individuality of consciousness, is displaced or replaced by dependence on a 'higher authority' (e.g. hypnotist, demagogue, demon, or voice). The process is culturally variable. Jaynes listed four aspects of the paradigm:
 * 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.

In the modern world, some cultures treat voice-hearing positively, making room for both voices and normal consciousness, while others negatively treat voices as a disruption.

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?” In 2021, however, philosopher Susan Blackmore described Jaynes's description of the problem of consciousness as one of the best. 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."

In 2016, Marcel Kuijsten argued 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".

The 'split-brain' criticism
A claim has been made that the bicameral mind was some sort of 'split brain'. The same point has been made as a criticism, 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" and 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 the cerebral hemispheres differing, 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 an ancient 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 does not show 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."

About 'consciousness'
Some have been quick to reject Jaynes's arguments based on their own, often vague, preconceptions rather than his detailed discussion of the problem of consciousness, and his 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 by language as a of consciousness over a lifetime of remembered 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 major feature of consciousness, namely "narratization", which is tied to the notion of the 'Self', while its role in volition is limited. Jaynes argued that right-hemisphere "narratization in epics" was first based on writing, and was how the bicameral 'gods' organized memory of their own "god-commanded events". In consciousness, however, narratization is how pieces of experience and memory become connected into large patterns that can 'make sense' of behavior or to some degree 'inform' unconscious processes but not 'control' them.

Oakley and Halligan, the authors of a 2017 paper, affirm a 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."

For Jaynes, the problem of understanding consciousness had always been one of finding a good metaphor for consciousness, that is, finding something that consciousness is like. The difficulty is that there is nothing in the 'outside world' that is like consciousness. Jaynes "sketched out" his "somewhat rough-hewn beginning" of the complex linguistic basis of consciousness and its various features, and he summarized as follows: "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 repository. And it is intimately bound up with volition and decision."

Elsewhere: "Conscious mind is a spatial analog of the world and mental acts are analogs of bodily acts. Consciousness operates only on objectively observable things. ... there is nothing in consciousness that is not an analog of something that was in behavior first.  ... consciousness is [the] invention of an analog world on the basis of language, paralleling the behavioral world even as the world of mathematics parallels the world of quantities of things[.]"

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 doubts that 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.

Bicamerality is "secular 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 wrote 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" rather than science, 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 criterion 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". Mooneyham-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 Mooneyham-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. Jaynes apparently affirmed 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." Mooneyham-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." She argued that the discontinuity Jaynes "tolerates" is not metaphysical, but exists "in terms of natural science alone": that the divide between bicamerality and consciousness is a consequence of "complex social relationships" and language; that Jaynes's work is a "monumental critique" and rejection of metaphysical explanations for both religion and consciousness; and 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: that 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 twice says of it, "this essay is no exception." According to Mooneyham-White, Jones's criticism "seized upon [this admission] as crucial evidence of the unscientific nature of Jaynes’s ideas." But Mooneyham-White concluded that Jones's position may have come from a rival scientism that cannot allow any discontinuities, and cannot recognize its own dependence on "the necessary relationship between any comprehensive scientific theory and [a system of] belief."

Research
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. One early study, in 1982, had some supportive results 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 discussed in The Lancet and the Journal of Psychiatry and Neuroscience in support of Jaynes’s theory. As of 2020, the brain's language system is known to be more complex than it seemed in the 20th century "classical model", and the right hemisphere has a known distinctive role in both linguistic and non-linguistic communication. A number of competing models exist to describe and explain verbal hallucinations. An "abnormal asymmetry" involving abnormal right hemisphere activity has been linked with severe schizophrenia but more with its distress than with voices, and the 'hearing of voices' is not necessarily a disorder or disease. The simple neuropsychological model proposed by Jaynes for ancient voices might not explain all the phenomena — neurological, phenomenological, cultural — of modern verbal hallucinations, and the right hemisphere's role remains controversial.

The 'split-brain': one mind or two?
Since the 1960's, the study of so-called "split brains" was enabled by surgically "cutting the corpus callosum," and has been a major source of knowledge about the abilities of each hemisphere and the differences between them. Much remains to be learned about how the hemispheres interact in the normally connected, healthy brain.

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 is interpreted to indicate 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.

Hemispheric asymmetries, cerebral torque, and plasticity
Anatomical hemispheric asymmetries, which are found in many species, are thought to correlate with "lateralized specialization" of functions that provide evolutionary advantages, 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 hemispheric asymmetries in common, the greater degree of asymmetry in the human brain seems generally indicative of higher human abilities such as language.

One major hemispheric 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."

While both sides resemble each other at the macrostructural level, they differ developmentally, and the brain may mature into varied "types" of hemispheric functional organization. Different cognitive processes can lateralize in different ways, accounting for "reversed asymmetries or the absence of asymmetry" as well. As of 2019, functional and cognitive consequences of anatomical asymmetries require further study, and research has focused on comparing variability of 'normal' and 'atypical' cerebral asymmetry.

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. Atypical degrees of torque have been associated with atypical specialization of hemispheric functions.

Right-hemisphere language
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]."

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.

Phenomenology of 'voices'
The term, which implies all kinds of 'sound-like' phenomena, is often used interchangeably with AVH (auditory verbal hallucination) which means "voices" (as in the quotations below). Voices are the most common sounds 'heard'. 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, ... the temporal cortex [is] 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'. Voice-hearing is often associated with and harmful behaviour, but can sometimes be personally meaningful, and some cultures regard voices, whether positively or negatively, as spiritually significant.

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

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."

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.

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" to present "converging evidence for an interhemispheric miscommunication due to [excitatory-to-inhibitory] imbalance as one correlate of AVH[.]"

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.

As of 2014, how the corpus callosum regulates inter-hemispheric communication remains uncertain.

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[.]"