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The Origins of LanguageJordan Zlatev

Lecture 5Body and brain for language

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Projects

Spell out your main question(s). Make sure that it is relevant to language origins!

Define your main terms: “language”, “gesture”, “cognition”, “adaptation”, “culture” – at least provisionally

Describe previous answers – theories: briefly.

Evaluate against evidence. Conclusions – and if necessary,

revise (discuss) definitions again!

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Reprise from Lecture 4

“The uniform language capacities of all human populations today prove that all adaptations for language… must have been in place” not LATER than 100,000 years ago…”

But: when, how and why did they appear?

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Prerequisites for language

In bodily anatomy In brain structure

Main method look for differences between “us and

apes” that seem to be adaptations for language - and other specifically human forms of communication

Try to trace their origins on the basis of paleo-anthropological evidence (“stones and bones”)

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Possible adaptations for

1. Speech production2. Speech perception3. Brain size and organization

1. Lateralization2. “Modularity”3. Extended mirror neuron system

(Arbib 2005; Zlatev 2008)

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1. Speech production

“The larynx works like a valve, opening and closing to let air pass. When it is shut, food can pass into the esophagus at no risk to the lungs. The best place for such a seal is right at the top of the trachea so that no food or drink accidentally goes even a little ways down it, but humans have a second use for the valve. We work it like a musical instrument shaping the sounds made by passing air as we speak. The musical valve works best if we pull it a bit down into the trachea so that the air wave shaped by the larynx can resonate before leaving the mouth.”http://ebbolles.typepad.com/babels_dawn/2006/10/the_human_laryn.html

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The descent of the larynx “At birth the human larynx is in the normal, animal

location, enabling babies to nurse without risk of choking.

The larynx typically begins to move lower at about three months of age and reaches its final position by age four. People familiar with children’s speech will notice that the start of the relocation is also when infants start to coo. The end is about the time the children finally become clearly intelligible to well-meaning strangers.

The lowered larynx lets humans produce a much wider variety of sounds, particularly vowel sounds, than apes can generate.”

http://ebbolles.typepad.com/babels_dawn/2006/10/the_human_laryn.html

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Descent of the larynx

“a two step process” (:78) The laryngal skeleton relative to the hyoid

bone: also in chimpanzees The decent of the hyoid bone (possibly

unique to H. sapiens – but only among the primates! (Fitch 2002)

Actually: a three step process! Sexual selection, in part – a second descent

in males in puberty (as in some deer) Either exaptation or adaptation for speech

(to outweigh the risk of choking)

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Descent of the larynx

When? Neanderthal hyoid bone similar to sapiens

=> back to the common ancestor: H. heidelbergensis or H. Ergaster? 0,8 or 1,7 MYA?

If at least in part an adaptation for speech (i.e. not only an exaptation): “our ancestors had some form of spoken language before they had a human vocal tract” (: 80)

(evolution does not plan ahead)

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Conscious control

Pathways from neocortex to vocal cords in H. sapiens, but not in other apes: “removal of selection for [only] innate automatic vocalizations, leaving room for vocal learning to develop” (:81, cf. Deacon on devolution)

Enlarged hypoglossal canal: present at least in “later Homo”, but very possibly earlier - unclear conclusions

Motor neurons down the spine to the thorax (region from the neck to the diaphragm), but absent in H. ergaster (MacLarnon & Hewlitt 1999) – most important concrete evidence

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Control of rapid sequencing “Specific language impairment” (SLI), now being

often called “Familial language impairment” (FLI)

Defective gene FOXP2: “the language gene”More recently: “severe impairment in the selection and sequencing of fine orofacial movements which are necessary for articulation” (:83)

Two functional mutations in FOXP2 in the human line (different from the chimpanzees) – but when?

Broca’s area, basal ganglia and cerebellum are involved in non-speech sequencing (action, gesture, song…)

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“When did we start to speak?” Descended hyoid bone (second step in the

lowering of the larynx) Enlarged hypoglossal canal (better control of the

tongue) FOXP2 gene identical to H. sapiens (articulation

and other sequences), (Krause et al. 2007)… are all present in H. Neanderthalensis => “some type of speech must have been present

in our last common ancestor with the Neanderthals, 500,000 years ago or so, though fully human speech with all our articulatory capacity need not be much older than 100,000 years” (:85)

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2.Speech perception

Categorical perception for calls, and even human phonemes is observed in apes and monkeys: similar to children – not uniquely human.

Speech perception involves neural patterns of activation different from other sounds (though not a “module”).

Some “fine tuning” for improved perception of 2-4 kHz: typical for speech. Present in H. heidelbergensis (0,4 MYA) => Neanderthals

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3. Brain size (and organization)

Absolute and relative (brain/body ratio) increase of brain size: first in H. ergaster, then in H. neanderthalensis and H. sapiens)

Disproportionate increase in some areas: Prefrontal lobes, auditory-parietal areas (“Perisylvian cortex”), cerebellum (see p.92)

Neotony: rapid-growth rate is prolonged to childhood (“premature born apes”), favouring neocortex and (social) learning

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Brain evolution: why?

The brain: high metabolic cost and dangerous child birth – what is the evolutionary benefit?

By-product of growth and “weaker jaw muscles”?? “Cooling device”?? Surplus energy and smaller gastrointestinal tract? “Environment driven” (fruit, navigation, tools) “Socially driven” (“politics and coalition-building

are important for a primate’s success”, :97) Language/communication-driven: language-

brain co-evolution over 4 MY (Deacon 1997)

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Lateralization

Is language “located” in the left hemisphere? RHS is involved in prosody, word learning,

discourse processing, gesture, even grammar + plasticity (epigenetic development)

Still: evidence for anatomical (large “pyramidal neurons”) and behavioral (handedness, pointing, signing) asymmetries

But: such asymmetries are to some extent also in found in chimpanzees

Endocast of H. ergaster: enlarged Broca’s area

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Modularity

No evidence whatsoever of “encapsulated” modules (Fodor 1983), No “Big Modules”

Low-level sensory processing in specific areas, but: interconnected, interactive not genetically determined!

The classical “language area”, Broca’s area (Brodman areas 44, 45) in the left premotor cortex: involved in control of action, imitation, gesture… “convergence of audio-visual-motor processing streams” (: 110): multimodal coordination?

The “language” or even “grammar” gene FOXP2… see video

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SLI, K family, FOXP2

Observe the 6 minute excerpt from “What Makes Us Human? Part 2” BBC

Do the difficulties of the members of the K-family (and the boy who helped find FOXP2) seem to do specifically with “syntax”, or even a module within syntax?

From the little said about FOXP2 – does it seem a likely candidate for a “language gene”?

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A different kind of breakthrough?

“The discovery of mirror neurons in the frontal lobes of monkeys, and their potential relevance to human brain evolution … is the single most important "unreported" (or at least, unpublicised) story of the decade [i.e. the 1990s].

I predict that mirror neurons will do for psychology what DNA did for biology: they will provide a unifying framework and help explain a host of mental abilities that have hitherto remained mysterious and inaccessible to experiments.”

(V. Ramachandran HTTP://WWW.EDGE.ORG/3RD_CULTURE/RAMA/RAMA_P1.HTML

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”Mirror” and ”cannonical” neurons in macaque brain area F5

Canonical neurons: active only during the monkey’s own movements/actions

Mirror neurons: active both during execution and observation of similar movements/actions

(Rizzolatti et al. 1996)

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Basic monkey ”mirror neuron system”

F5: area in premotor cortex

AIP: anterior intraparietal area

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MNs: Great expectations! It is amazing how these cells have been

proposed as a solution to just about every mystery in the human mind: from empathy to imitation, mind-reading, language (evolution), autism, and even sexual preferences!

It is not surprising that their role has been regarded as much over-rated by some researchers in the field (Preson & de Waal 2002; Donald 2005; Csirba 2007).

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MNs: problems

Directly recorded only in monkey brains, with only indirect evidence for human brains.

Not sufficient for either ”simulation” (on any level) nor representation (or signification):X stands for Y for subject S

Present in macaques, while monkeys can neither imitate, gesture, nor use language…

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A possible neural basis for bodily mimesis and language

From ”mirror neurons” to neural circuits, involving multimodal perception-action cycles...

Basic idea: gradual evolution of the monkey mirror system for manual actions (similar to Arbib 2005, 2008) – but with a few important differences (more on this when discussing ”Stages”, Lecture 11)

Mimesis

“Mimetic skills or mimesis rests on the ability to produce conscious, self-initiated, representational acts that are intentional but not linguistic.” (Donald 1991: 168)

Mime, gesture, imitation, skill, mimetic imagination

A domain-general adaptation (in Homo ergaster), possibly initially for tool use, and then extended to communication

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The Mimesis Hierarchy (Zlatev 2005, 2007, 2008)

Level Acts and states

Language … dividing (semi)compositionally into meaningful sub-acts that systematically relate to other similar acts (as in grammar)

Proto-language … that are conventional-normative

Triadic mimesis(Intentionally communicative)

… intended to stand for some action, object or event for an addressee (and for the addressee to recognize this intention)

Dyadic mimesis(Not intentionally communicative)

… under conscious control and corresponding to – either iconically or indexically – some action, object or event, and at the same time differentiated from it

Proto-mimesis … involving cross-modal mapping between exteroception (normally dominated by vision) and proprioception (normally dominated by kinesthetics)

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1.Proto-mimesis: basic ”resonance”

Mirror neurons are part of a frontal-parietal-temporal system in the monkey brain

Responding to an open-ended set of manual actions

Basis for emulation: anticipating the results of others’ actions (without ”theory of mind”)

Possibly: basis for (simple) empathy, and contagion (mimicry), see video

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2. Dyadic mimesis: imitation and reenactment

The perisylvian cortex (and the prefrontal cortex) have expanded most in the human brain compared to apes (see Deacon 1997)

Moneky F5 -> Human BA 44 (pars opercularis of the inferior frontal gyrus)

Moneky PF -> Human inferior pariatal lobule (involved in tasks of imaginatory reenactment)

Moneky ST -> Human Superior Temporal Sulcus (involved in the analysis of biological motion)

-> And on the basis of behavioral and anatomical data: in apes too!

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”Expanding” the moneky MNS

STS

Broca

IPL

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2.Dyadic mimesis: neural adaptations?

Segregation of BA 44 into a dorsal part (for action) and a ventral part, source of an ”efferent copy” active only during imitation (Iacoboni 2005)

Lateralization right IPL active when imagining the motion of others, left IPL

when imagining self-motion Superior temporal sulcus (STS): analysis of other’s motion

(left HS) and ”in relation to the self” (right HS)

Quite possibly: prior to the evolution of language: some degree of handedness in chimps, and evidence for lateralization in Homo ergaster

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3.Triadic mimesis: iconic gestures and pointing

Moneky F5 mirror neruons do not repsond to ”intransitive” (non-object related) actions

By supporting imitation, the extended ape (common ancestor) MN system would support this, at least to some extent (apes better than monekys in imitation, less so than us)

Further extending, and differentiating between expression and content along with lateralization: iconic gestures (pantomime): the first true signs?

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3.Triadic mimesis: iconic gestures and pointing

McNeill (2005): the content (imagery) of gestures is based on RH-activity, their ”orchestration” mainly on LH (”Broca’s area”)

Gestures for non-present actions and objects would presuppose extended lateralization (at least by Homo heidelbergensis)

Combining iconic gesture and pointing: ”proto-predication”: (Point-X, Iconic-gesture-X) (but not ”gestural language”)

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4.Proto-language

Segregation of BA 45 (heteromodal) and BA 44 (primarily for speech)

An important function of vocalization: to ”disambiguate” and conventionalize iconic gestures

BA 4a and BA 6 in ventral pre-motor cortex (PMv) – active during both production and perception of meaningless syllables (Wilson et al 2004), support for the ”motor theory of speech perception” (Leiberman et al 1967)

Wernicke’s area (= superior and middle temporal): homologue of monkey PF (Arbib 2005)? Not really...

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”Wernicke’s area” – a novel adaptation, facilitating speech/sign comprehension?

Wernicke

STS

Broca

IPL

”…Wernicke’s area as combining capabilities for recognizing protosign and protospeech to support a language-ready brain that is capable of learning signed languages as readily as spoken languages” (Arbib 2005)

H. sapiens (sapiens)BA 44, 45 = “Broca”BA 22, 39, 40 = “Wernicke”

Overlap extensively with the “human mirror neuron system” (Arbib 2005; Iacoboni 2005; Decety & Chaminande 2005): in tasks of perception-action matching, imitation, imagination, pantomime…

BA 4, 6 = perception-production of “meaningless syllables” (Wilson et al. 2004)

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An extension of control for bodily mimesis to “vocomimesis” and eventually phonology (Zlatev 2008b)

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5.Language (vocal or signed)

Exaptations for hierarchical structure for action and imitation (involving not only the extended MNS, but basal ganglia, pre-SMA and cerebellum)

Grammar proper: from protolanguage (over the last 100 000 years) on the basis cultural and linguistic, ”post-biological” evolution (Arbib 2005)

All form-classes (e.g. adjectives, prepositions, affixes) can be potentially traced back to either object-words (nouns) and actions-words (verbs) (Heine and Kuteva 2002, 2007)

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Modern languages

A product of a longer period of brain-culture co-evolution (6 000 000 – 200 000 YA) + a shorter period of cultural-linguistic evolution (200 000 – present): are all languages equally complex?

”…no powerful syntactic mechanisms need have been encoded in the brain of the first Homo sapiens. Rather it was the extension of the imitation-enriched mirror system to support intended communication that enabled human societies, across many millennia of invention and cultural evolution, to achieve human languages in the modern sense” (Arbib 2005: 123)

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Finally…

There may be other adaptations, less directly related to language, but preparing the (long) road towards it…