Consciousness, the Threshold Between Mind and Matter

“Ours is a world of words: Quiet we call

Silence — which is the merest word of all.” Al Aaraaf by Edgar A. Poe

One of the most characteristic abilities of humans is the ability to produce and understand complex language that is primarily abstract and metaphorical in nature. This stands in stark contrast to the gestures and innate calls of other animals which are reactive in nature, that is to say animals can only communicate about items in their immediate environment while human speech doesn’t rely on environmental triggers.[1, 2] Since the early development of language didn’t leave a distinct archaeological record which can be examined, in order to study its development we must examine physical evidence such as the tools left behind by early man as well as neurological studies, many of which compare the brain of man to that of closely related primates.

Hominins have been using stone tools for at least 2.6 million years, the earliest of these were made by using a hard cobble, known as a hammerstone, to strike off flakes from a softer piece of stone known as a core.[See image below, Figures 1, 2, Video 1] These early stone implements are referred to as Oldowan tools, despite being simple flakes and choppers which were only worked on one surface they were in use for almost one million years. It’s unclear which hominin species initially created these tools, but one thing which is clear is that multiple species ended up using them, including several members of the Homo family including H. australopithecus, H. habilis, H. ergaster, and early Homo erectus.[3] These simple implements were gradually replaced by the more advanced Acheulean tools starting around 1.75 million years ago– an important note here is that the older tools continued to be used, and manufactured, despite the advancement.[4] Acheulean tools, which were predominantly pear-shaped handaxes, were worked symmetrically on both sides so that they could fit in the palm while also having a much larger cutting surface, this level of attention to detail and standard form seems to indicate a great cognitive stride had been made.[See Figures 3, 4, Videos 2, 3] Whereas early stone tools required only a single hammerstone, the production of Acheulean handaxes is a multistage process which required at least two types of hammerstones, a coarse stone for abrasion, and a baton made of antler, bone, or wood, for knocking thin flakes off of the stone.[5, See Figure 5]

Oldowan Chopping Tool

Oldowan Chopping Tool

Acheulean Handaxe

Acheulean Handaxe

When you compare the simple pebble tools of the Oldowan Industry to those of the Acheulean it becomes obvious that these later tools require much greater motor skill, a knowledge of the properties of stone, and also careful planning in order to create an intentionally shaped tool.[5] In a detailed analysis of the Oldowan Industry from a primatologist point of view Wynn and McGrew (1989) came to the conclusion that “all the behaviour that can be inferred from Oldowan tools and sites falls within the range of the ape adaptive grade. There is nothing exclusively human-like about this oldest known archaeological evidence.”[6] The authors of the study made this assessment based primarily upon how early stone tools could be manufactured using simple spatial concepts, they aren’t symmetrical, and could be created by repeatedly striking a hammerstone against a core/cobble within close proximity– living apes follow similar procedures to create various tools which they employ. In contrast, Acheulean tools were worked symmetrically on both sides, and many of these tools incorporate hand/finger grips, rounded ends to distribute shock over the entire palm, and even centrally located fossils which may indicate aesthetic concern.[See examples 7, 8, 9, 10, 11, 12]

From knapping to language to the conscious mind

Historical Development of Toolmaking Industries, and Jaynes’ Proposed Timeline of the Development of Speech

Many anthropologists consider the use of symbols to be an essential if not defining aspect of culture, which has been defined by the founder of cultural anthropology Edward B. Tylor as “that complex whole which includes knowledge, belief, art, morals, law, custom, and any other capabilities and habits acquired by man as a member of society.”[13] Anthropologist Ralph L. Holloway, Jr. stated that the definition of culture should also include the “imposition of arbitrary form upon the environment” as “these two attributes are specific and unique to human behavior, and they can be identified by the appearance of stone tools in the archaeological record.”[14] An important characteristic of the tools of early man is their non-iconic nature (indicated by the term arbitrary form), when you compare these early tools to those of animals you see that even the tools of primates are iconic, as in a stick used for fishing for termites is still a stick despite having the leaves removed from it. In contrast, the standardized form of Acheulean tools indicates that there are systematic rules which one must follow in order to transform a stone into a handaxe– Holloway points out that these chained actions are a type of grammar consisting of a “basic “vocabulary” of motor operations– flake detachment, rotation, preparation of striking platform, etc.” Holloway describes the grammar of tool-making in greater detail in the following section:

Returning to matters of syntax, rules, and concatenated [chained] activity mentioned above, almost any model which describes a language process can also be used to describe tool-making. This is hardly surprising. Both activities are concatenated, both have rigid rules about the serialization of unit activities (the grammar, syntax), both are hierarchical systems of activity (as is any motor activity), and both produce arbitrary configurations which thence become part of the environment, either temporarily or permanently.

An important component of culture is the feedback cycle created by the tools, or arbitrarily structured environment, as the “altered environment shapes (man’s) perceptions, and these are again forced back upon the environment, are incorporated into the environment, and press for further adaptation.” So early man shapes a rock into a tool and in the process of doing so he shapes his own brain (neural networks, etc) and then once the tool is used it changes how man interacts with the environment which then gives feedback as to its efficiency.

Over the last few decades several interesting studies have examined the functional difference in Oldowan versus Acheulean tool-making as well as the importance of stone knapping toward the development of early language, these studies have shone light on the dark recesses of the Early Stone Age (ESA). One particular study used a type of neuroimaging, fTCD, which measures changes in cerebral blood flow to determine which areas of the brain were activated while completing one of two tasks, creating an Acheulean handaxe or a language task.[15] The findings of the study are summed up in the following section:

Making an Acheulean handaxe requires both working memory and planning memory. This careful planning is dominant in the initial phase of each experimental block in our study. This action planning draws on brain areas that are shared with language tasks, such as the left-lateralized ventral premotor areas and Broca’s area. Our subject pool shows highly correlated individual brain blood flow lateralization in the early phases of task execution for both tasks. Our findings add empirical data to the hypothesis that action planning for tool-making and language draw on shared functional brain structures. The correlated time-signatures for Acheulean knapping and language, which remain significantly correlated within subjects despite variability between subjects, indicates that the same brain networks are being activated for both tasks. They suggest that tool-making and language share a basis in more general human capacities for complex, goal-directed action.

This study demonstrates that language and tool-making share the same neural pathways, perhaps this is because of the countless generations of hominins activating these networks with the orderly, precise techniques required for Acheulean tool-making– as Princeton psychologist Julian Jaynes said “There is nothing in consciousness [introspectable mind-space] that is not an analog of something that was in behavior first” and likewise, there is no symbolic language without its physical precedent, syntax. [See schematic diagram for “Brain regions activated during speech and action observation, tool-use, word generation, and Acheulean knapping”]

Another interesting study used a different type of neuroimaging, PET, which produces real-time three-dimensional images of the brain to map out the areas which are being used by an activity, in this case it was either Oldowan or Acheulean toolmaking by expert subjects.[5] The subjects were all “professional archaeologists with more than 10 years stone toolmaking experience and already familiar with Oldowan and Late Acheulean technologies,” their tasks (which were divided over three days) were to create Oldowan-style tools, Acheulean handaxes, and a control task in which they were instructed to strike cobbles together without using any specific toolmaking techniques. Upon reviewing the results, the researchers noted that, “As expected, expertise was associated with increased IPL [Inferior Parietal Lobule] activation during Oldowan toolmaking. However, contrary to expectation, this activation was strongly bilateral.” They went on to say that it appears that improved handaxe creation is a result of more accurate neural representations of the body-tool combination, and not a consequence of enhanced motor planning/strategy as they had expected. The enhanced sensorimotor representations of the tool-body system could perhaps have been developed through the millennia as hominins worked with stone tools, leading to what is essentially a more accurate neural analog of the body.

Language Areas of the Brain

Language Areas of the Brain

The primary area of the brain related to tool usage is the Inferior Parietal Lobule, the left IPL is located at the meeting place of the auditory, visual, and somatosensory (touch, temperature, pain, and limb position) cortexes and it is deeply connected with all of these structures. Because of these connections, the IPL is one of the primary areas for processing auditory and visual information and it is particularly important to language comprehension and mathematics– as well as memory retrieval, attention, and theory of mind.[16] The right IPL, on the other hand, “organizes many spatial functions for both sides of the body and for both sides of external space.”[17] The IPL is divided into two parts, the Supramarginal Gyrus and the Angular Gyrus, the AG is associated with complex language functions like reading, writing, and interpreting the meaning of writing; pioneering neurologist Norman Geschwind hypothesized that this area was responsible for translating written word to internal monologue. The right AG is responsible for spatiovisual attention as well as maintaining an awareness of the self through monitoring intended actions and the resulting actual movement, the discrepancy between these two allows the AG to maintain an awareness of the self.[18] While not as involved as the AG, the Supramarginal Gyrus, or SMG, assists in language perception and processing, as well as being a part of the previously mentioned somatosensory cortex of which the SMG is particularly important in the perception of space and the location of limbs. The SMG is also a part of the mirror neuron system which is made up of neurons which are activated when an animal performs a specific action or observes another performing the same action. A recent study conducted using fMRI found that both humans and monkeys have activity in corresponding regions of the brain when observing hand actions and actions performed using simple tools, but in the humans there was additional activity in an area at the front of the left SMG (the left aSMG) while viewing actions performed using tools.[19] The authors of the study stated that the activity in the left aSMG was only present when observing “goal-directed action performed with a mechanical device, vanishing when the goal of the action was omitted from the videos,” this led them to believe that the area had evolved specifically for tool use.

Although both hemispheres are used for language to some degree, in the majority of people (approximately 97%[20]) the left hemisphere is the one where most linguistic processing takes place while the right hemisphere deals with minor functions like intonation/accentuation, prosody, pragmatic, and contextual aspects of language.[21] The areas of the brain involved in language are more numerous than once thought, but the three major areas are Broca’s Area, Wernicke’s Area, and the Inferior Parietal Lobule. A fascinating feature of the cerebral hemispheres is pointed out by neurologist Joseph LeDoux in the following quote:

The primary functional distinction between the human hemispheres thus involves the differential representation of linguistic and spatial mechanisms: These mechanisms, moreover, are selectively represented in restricted zones within each half-brain. It is of particular interest to note that while the IPL in the left hemisphere is involved in linguistic processing (see above), the right IPL is involved in spatial processing. Thus, the two functions that comprise the primary functional axis of brain asymmetry are dependent, in part, upon the integrity of homologous areas in opposite hemispheres. This complementary organization of IPL in the two hemispheres is, I believe, an important clue to the origin of human brain asymmetry.

The story begins to unfold when we consider several factors discussed earlier: Spatial mechanisms are represented in both the left and right IPL in nonhuman primates and these mechanisms are similar in many respects to the spatial functions of the human right IPL. Given that the nonhuman primate IPL and the IPL in man’s minor hemisphere are homologous brain structures related through common ancestry (see LeDoux, 1982, for discussion) an important insight emerges: In man, language is represented in a region (IPL) of the major [dominant] hemisphere which, in the minor hemisphere, is involved in spatial functions, and was involved in spatial functions in both hemispheres of man’s ancestors.[For background info on the terms major and minor hemisphere see Note 1] The unavoidable conclusion of this line of reasoning is that the evolution of language involved adaptations in the neural substrate of spatial behavior.[17]

This quote has particular importance to a theory of the origin of human consciousness called the Bicameral Theory of Mind, the creator of this theory, Princeton Psychologist Julian Jaynes theorized that thousands of years ago the human mind was divided into two chambers.[If you’re not familiar with the Bicameral Theory of Mind please read the short summary here: ] One of these chambers was used for basic functions which the individual had either been taught by their culture (like hunting, making shelters, etc) or learned and repeated many times while the other area was only used in the rare circumstance that a person encountered a completely novel, dangerous situation. This type of person was said to be bicameral, they lacked the ability to introspect or reason with logic so when they encountered a situation like a bear suddenly emerging from a cave nearby the other chamber of their mind would use past experience and tell the man side of the mind what to do– this was experienced as an auditory hallucination, and if this seems hard to believe then one needs only to look at the number of people today who experience hallucinations when under severe stress or isolation. When reviewing the studies which were cited previously with this theory in mind an interesting picture begins to develop, but before surveying this we should turn to a paper which was referenced by the PET study of Oldowan and Acheulean toolmaking. In a paper titled Functional Precursors to Language and its Lateralization the authors describe how language has a “frame-content mode of organization: at the phonological level, consonant and vowel elements are inserted into syllabic frames; and at the morphological level, stem forms of content words are inserted into syntactic frames.”[22, See image below] The authors of the paper then go on to propose that lateralization of brain function developed first for bimanual coordination, as is seen with stone toolmaking, before being used for language. Returning to the task at hand, the previously mentioned PET study stated that the function of the non-dominant hand is “not simply to execute gestures more typically done with the dominant hand but rather to properly position and support the core to receive the action of the dominant hand.”[5] In other words, the content, or dominant hand, acts upon aspects of the environment which are framed, or held carefully in place, by the non-dominant hand; in this context, what is described here is what could be referred to as the Frame-Content Phenomenon where the dominant hand, which is usually the right one, would act upon the environment in a very direct way while the non-dominant hand would react to the actions of the dominant hand and the subsequent change cascade caused in the environment (mathematically that would be: the actions of the Right Hand + the change/resistance induced in the Environment + Past Learning + spatial detection = Left Hand reaction/movement). This has a specific significance to the Bicameral Theory of Mind, as the dominant hand would essentially be the hand of man while the non-dominant would be the hand of god; Jaynes described the hallucinatory god voice as being made up of “stored-up admonitory wisdom,” and this past learning would be a part of my proposed formula, but there are other factors as well– all of which are characterized by the visual aspect of the right hemisphere, like current visuospatial processing and encoded visual memories which rely on a steady mental frame, aspects of which were learned, while other features were inborn.

From Frame to Content, from Matter to Mind

Frame-Content Theory of Language

The IPL contains what are referred to as multimodal neurons, these neurons are capable of processing various senses simultaneously instead of being specialized for a single function like most neurons. This would seem to be essential for their proper function as the left IPL is located at the meeting place of the auditory, visual, and somatosensory cortexes where it acts as a bridge for the integration of the various senses.[16] Renowned neurologist V.S. Ramachandran has written about how he considers a portion of the IPL, the Angular Gyrus, to be critical to the understanding of metaphors because of its multimodal nature and position at the juncture of the various cortexes[23]. Some linguists consider language to be built from metaphor as there would be a limited number of possible utterances if an individual were to only use words in their most literal sense, but metaphor carries meaning from one object to another because of some similarity between the two. Many metaphors are cross-modal, as in a sharp cheese, loud shirt, or bitter cold, the reason for this would seem to be because we label the unknown in the terms of the known– this labeling would seem to be an essential quality of subjectivity, and interestingly the Angular Gyrus has been shown to “be directly involved when you assign a name to an object or when you read its name.”[16] According to the Bicameral Theory of Mind, metaphor was essential to the development of consciousness, which Jaynes defined as “that which is introspectable,” or “an analog ‘I’ narratizing in a functional mind-space.” What exactly is a functional mind-space, and what does metaphor have to do with it? Since a metaphor transfers the usage of one term, or phrase, to describe something else because of a perceived similarity of the two things, or because of a certain relationship which the objects share, it allows one to distill the essence of something so that it can be easily communicated to someone else– in a similar way metaphor could allow for the easier mental manipulation of what would otherwise be too complex to process, or store in short-term memory. [For an in-depth discussion of the importance of metaphor toward consciousness see my previous post:]

A 2010 meta-analysis of the literature on laterality of motor control by Charleston neurologist Iraj Derakhshan came to a surprising conclusion, that Newton’s theory of the laterality of the brain is incorrect. In short, Newton’s theory is that “each hemisphere controls movements of the other side of the body and that the sensations arising from each side achieve consciousness in the opposite hemisphere; i.e. that there are two “endpoints in visuomotor stream,” one for each side of the body”[24] This theory has been accepted for over 300 years as a result of its simplicity, and also because Newton had such a profound influence on physics and mathematics. By providing numerous pieces of evidence after carefully reviewing clinical and experimental literature Dr. Derakhshan demonstrated that

“brainedness (i.e. the laterality of the executive hemisphere) stands for the destination of all signals achieving consciousness and that the minor hemisphere represents three-dimensional reality of space. Awareness to that reality, however, awaits arrival of signals arising from the nondominant side of the body/space to the major hemisphere via the posterior aspect of the callosum.”

The studies presented previously demonstrate that the right hemisphere is specialized for visuospatial processing, and is similar in many ways to that of both hemispheres of the nonhuman primate, while the left hemisphere is specialized for linguistic processing, syntax, and time, so it would be safe to say that at one time both hemispheres of man were utilized for visuospatial processing and that as language developed it began to build upon the previous functions/structure of the left hemisphere. As this process was happening, likely over a span of hundreds of thousands of years and numerous different species of hominins, the left hemisphere became the place where reality was distilled/subjectified, in the sense that a map, for example, relies on spatial coordinates where the distance between two points is objective (though some maps are more accurate than others, they are still created to represent a specific terrain which should be very similar from case to case) while a novel object, situation, art, etc is always dependent on past experiences and language. Thus we see that the fundamental function of the right hemisphere is to “represent three-dimensional reality of space,” while the role of the left hemisphere is to learn and process language which allows for an awareness that can then be used to subjectively pilot the machine.

Derakhshan’s One-way Callosal Traffic Theory has profound implications for Jaynes’ Bicameral Theory of Mind, but before elaborating on this I would like to draw your attention to the following quote from Jaynes:

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.(pg 55)[2]

Analog and metaphor are important parts of Jaynes’ theory, notice that these two functions are made possible by spatial and linguistic mechanisms respectively, once again this demonstrates the tendency of evolution to rebuild upon an already successful model, in this case the frame-content mode of organization. As spatial mechanisms are represented in the right hemisphere, and linguistic processing in the left, it would seem that the right hemisphere would construct a visuospatial analog of the world and the left hemisphere would act upon it with metaphor– just as ancient man struck stone cobbles together to create tools, post-linguistic man manipulates metaphors in mind-space so that he can not only construct possible futures, but examine the recreated past. Before early man acquired metaphor it would appear that he could not move through mind-space in this way, so he lacked introspection, reason, and the ability to examine the past, or consciously project possible futures, but it’s likely that experience was still constantly being taken in by the visuospatial networks of the mind which would calculate the best possible action/movement in a given situation and project this to the left hemisphere in times of need. When viewing the Bicameral Theory of Mind in relation to the One-way Callosal Traffic Theory one quickly notices that in both theories the same side of the brain is responsible for motor signals, these are referred to as the man side of the brain and the major hemisphere respectively, this is essentially the intermediary of the individual and the environment. The god side of the brain and the minor hemisphere are more of an intermediary between the individual and the past, and visuospatial calculation, neither of these aspects require language as they would rely on visuospatial processing to reconstruct visually encoded memories and/or calculate movement.

The picture which is beginning to develop is that for hundreds of thousands of years early hominins created some of their first tools primarily with their right hand, and subsequently left hemisphere, this specialized the motor cortex and other circuits to process syntax. After producing these tools for close to a million years a more advanced type of stonework took shape, this industry, the Acheulean, required much more precision and visuospatial processing skill, this enhanced the right hemisphere’s ability to “frame situations” or focus on what action would be the most likely to be successful, at least mathematically speaking. In a sense, the right hemisphere retained the animal/visuospatial mind as the left hemisphere became more and more accustomed to syntax, time, and subsequently language, thus we get the dualism inherent in the mind of man, where man is constantly in opposition to his animalistic nature. After millennia of framing situations so that man knew where to appropriately inject content he had reached a point where the non-conscious animal mind could be used as a divine source of guidance in times of need: a silent sentry that calculated not just the best possible movement for the left hand under certain conditions, but also the best possible course of action for the bicameral man in a dangerous situation by utilizing Wernicke’s Area (the right hemisphere area responsible for speech production) so that the individual would hear a command telling him what to do. As the conscious mind developed this focus was less strictly limited to specific situations, and manifested as inspiration from past events, both remembered and unremembered, and it could be occasioned by the use of certain drugs, meditation, stress, or other altered states of consciousness. There’s something indescribably beautiful about the left hand being both the hand of god, and of the animal mind, and I have no doubt that this is a large part of why so many ancient, and modern, cultures are biased against the left hand/side– the personal god, and man’s animal nature, stands in contrast to that of holy doctrine. [For more on the negative connotation of left-handedness, see Wikipedia: Bias Against Left-handed People]

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References Section
[1] Jane Goodall, who is considered by many to be the leading expert on chimpanzees (which are the closest living relative of humans), has studied primates extensively over half a century and had this to say about the usage of language by chimps: “What’s the one obvious thing we humans do that [chimps] don’t do? Chimps can learn sign language, but in the wild, so far as we know, they are unable to communicate about things that aren’t present. They can’t teach what happened 100 years ago, except by showing fear in certain places. They certainly can’t plan for five years ahead. If they could, they could communicate with each other about what compels them to indulge in their dramatic displays. To me, it is a sense of wonder and awe that we share with them. When we had those feelings, and evolved the ability to talk about them, we were able to create the early religions.”
[2] Deacon, T.W. (1997) The Symbolic Species: The Co-evolution of Language and the Brain. New York: W.W. Norton & Company, Inc.
[3] Richards, M. (2002). A Brief Review of the Archaeological Evidence for Palaeolithic and Neolithic Subsistence. European Journal of Clinical Nutrition, 56(12), 1270-1278. Retrieved March 3, 2015, from
[4] Beyene, Y., Katoh, S., Woldegabriel, G., Hart, W., Uto, K., Sudo, M., … Asfaw, B. (2013). The Characteristics and Chronology of the Earliest Acheulean at Konso, Ethiopia. Proceedings of the National Academy of Sciences, 110(5), 1584-1591. Retrieved March 7, 2015, from
[5] Stout, D., Toth, N., Schick, K., & Chaminade, T. (2008). Neural Correlates Of Early Stone Age Toolmaking: Technology, Language And Cognition In Human Evolution. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1499), 1939-1949. Retrieved March 10, 2015, from
[6] Wynn, T., & McGrew, W. (1989). An Ape’s View of the Oldowan. Man. Published by: Royal Anthropological Institute of Great Britain and Ireland, 24(3), 383-398. Retrieved March 18, 2015, from
[7]World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[8] World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[9] World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[10] World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[11] World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[12] World Museum of Man. (n.d.). Retrieved March 8, 2015, from
[13] Tylor, E.B. (1881). Anthropology an Introduction to the Study of Man and Civilization. London: Macmillan and Co.
[14] Holloway Jr., R. L. (1969). Culture: A Human Domain. Current Anthropology. 10(4). Retrieved March 10, 2015, from,+Jr.,+Culture.+A+Human+Domain.pdf
[15] Uomini, N., Meyer, G., & Petraglia, M. (2013). Shared Brain Lateralization Patterns in Language and Acheulean Stone Tool Production: A Functional Transcranial Doppler Ultrasound Study. PLoS ONE, 8(8), E72693. Retrieved April 14, 2015, from
[16] Dubuc, B. (2002). The Brain from Top to Bottom. Broca’s Area, Wernicke’s Area, and Other Language-Processing Areas in the Brain. Retrieved April 21, 2015, from
[17] LeDoux, J. (1984). Cognitive Evolution: Clues from Brain Asymmetry. The Right Hemisphere: Neurology and Neuropsychology (A. Ardila & P. Ostosky-Solis, Eds.), Vol. 1, 51-60. New York: Gordon and Breach. Retrieved April 21, 2015, from
[18] Farrer, C., Frey, S., Horn, J., Tunik, E., Turk, D., Inati, S., & Grafton, S. (2007). The Angular Gyrus Computes Action Awareness Representations. Cerebral Cortex, 18(2), 254-261. Retrieved May 24, 2015 from
[19] Peeters, R., Simone, L., Nelissen, K., Fabbri-Destro, M., Vanduffel, W., Rizzolatti, G., & Orban, G. (2009). The Representation of Tool Use in Humans and Monkeys: Common and Uniquely Human Features. Journal of Neuroscience, 29(37), 11523-11539. Retrieved May 31, 2015.
[20] Fitzpatrick, D. (2004). Language and Lateralization (D. Purves, G. Augustine, & D. Fitzpatrick, Eds.). Neuroscience. Sunderland, Mass: Sinauer Associates
[21] Seghier, M. (2012). The Angular Gyrus: Multiple Functions and Multiple Subdivisions. The Neuroscientist, 19(1), 43-61. Retrieved May 24, 2015, from
[22] MacNeilage P.F, Studdert-Kennedy M.G, Lindblom B. (1984). Functional Precursors to Language and its Lateralization. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, 246(6), R912-R914. Retrieved June 7, 2015, from
[23] Ramachandran, V.S., Hubbard, E.M. (2003). The Phenomenology of Synaesthesia. Journal of Consciousness Studies, 10(8), 49-57. Retrieved May 4, 2015, from
[24] Derakshan, I. (2010). It Is All Quiet in the Minor Hemisphere: A Fresh Look into the Laterality of Consciousness, Vision and Attention in Human Brain. Biomedicine International Journal, 1(1). Retrieved June 7, 2015, from

[Note 1] The terms major and minor hemisphere are used by many specialists to denote that one hemisphere doesn’t dominate the other, or that one hand is not more important than the other simply because it is more dexterous. Both hands are specialized to act in conjunction where each hand is essentially a motor and by using them together they work in a series.

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