on the neurocognitive basis of language sydney lamb l [email protected] 2010 november 12 wenzao ursuline...

On the Neurocognitive Basis of Language

Sydney Lamb

[email protected]

2010 November 12

Wenzao Ursuline College of LanguagesKaohsiung, Taiwan

Why is it important to consider the brain?

“I gather…that the status of linguistic theories continues to be a difficult problem. … I would wish, cautiously, to make the suggestion, that perhaps a further touchstone may be added: to what esxtent does the throry tie in with other, non-linguistic information, for example, the anatomical aspects of language? In the end such bridges link a theory to the broader body of scientific knowledge.”

Norman Geschwind “The development of the brain and the evolution of language” Georgetown Round Table on Languages and Linguistics, 1964

Topics

• A little neuroanatomy• Functional webs• Nodes and links: Cortical columns• Basic operations in the cortex• More operations: Learning

Topics

• A little neuroanatomy• Functional webs• Nodes and links: Cortical columns• Basic operations in the cortex• Syntax • More operations: Learning

The brain

• Medulla oblongata – Myelencephalon• Pons and Cerebellum – Metencephalon• Midbrain – Mesencephalon• Thalamus and hypothalamus – Diencephalon• Cerebral hemispheres – Telencephalon

– Cerebral cortex– Basal ganglia– Basal forebrain nuclei– Amygdaloid nucleus

Two hemispheres

Left Right

Interhemispheric fissure (a.k.a. longitudinal fissure)

Corpus Callosum Connects Hemispheres

Corpus Callosum

Major Left Hemisphere landmarks

Central Sulcus

Sylvian fissure

Major landmarks and the four lobes

Central Sulcus

Sylvian fissure

FrontalLobe

ParietalLobe

TemporalLobe

OccipitalLobe

Some brain facts – now well established

• Locations of various kinds of “information”– Visual, auditory, tactile, motor, …

• The brain is a network– Composed, ultimately, of neurons

• Neurons are interconnected– Axons (with branches)– Dendrites (with branches)

• Activity travels along neural pathways– Cortical neurons are clustered in columns

• Columns come in different sizes– The smallest: minicolumn – 70-110 neurons

• Each minicolumn acts as a unit– When it becomes active all its neurons are active

Deductions from known facts

• Everything represented in the brain has the form of a network– (the “human information system”)

• Therefore a person’s linguistic and conceptual system is a network– (part of the information system)

• Every lexical entry and every concept is a sub-network– Term: functional web (Pulvermüller 2002)

Primary Areas

Primary Somato-sensory Area

Primary Motor Area

Primary AuditoryArea

PrimaryVisual Area

Central Sulcus

Sylvian fissure

Divisions of Primary Motor and Somatic Areas


Primary Motor Area


PrimaryVisual Area

Mouth

HandFingers

Arm

Trunk

Leg

Higher level motor areas


Actions performedby hand


PrimaryVisual Area

Mouth

HandFingers

Arm

Trunk

Leg

Actions per-Formed by leg

Actions performedby mouth

Hierarchy in cortical development

Topics

• A little neuroanatomy• Functional webs• Nodes and links: Cortical columns• Basic operations in the cortex• Syntax • More operations: Learning

Hypothesis I: Functional Webs

• A word is represented as a functional web• Spread over a wide area of cortex

– Meaning includes perceptual information– As well as specifically conceptual information

• For nominal concepts, mainly in– Angular gyrus– (?) For some, middle temporal gyrus– (?) For some, supramarginal gyrus

Example: The concept DOG

• We know what a dog looks like– Visual information, in occipital lobe

• We know what its bark sounds like– Auditory information, in temporal lobe

• We know what its fur feels like– Somatosensory information, in parietal lobe

• All of the above..– constitute perceptual information– are subwebs with many nodes each– have to be interconnected into a larger web– along with further web structure for conceptual information

Building a model of a functional web:first steps

V

C

Each node in this diagramrepresents the cardinal node* of a subweb of properties

For example

Let’s zoom in on this one

M

T

*to be defined in a moment!

Zooming in on the “V” Node..

Cardinal V-node

Etc. etc.(many layers)

A network of visual features

Add phonological recognition

V

M

C

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imageT – TactileV – Visual

T

P

The phonological image of the spoken form [fork] (in Wernicke’s area)

These are allcardinal nodes –each is supportedby a subweb

Add node in primary auditory area

V

M

CT

P

PA

Primary Auditory: the cortical structures in the primary auditory cortex that are activated when the ears receive the vibrations of the spoken form [fork]

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imagePA – Primary AuditoryT – TactileV – Visual

Add node for phonological production

V

M

CT

P

PA

PP

For example, FORK

Labels for Properties: C – Conceptual M – Motor P – Phonological image PA – Primary Auditory PP – Phonological Production T – Tactile V – Visual

Part of the functional web for DOG(showing cardinal nodes only)

V

MC

T

P

PA

PP

Each node shown here is the cardinal node of a subweb

For example, the cardinal node of the visual subweb

An activated functional web(with two subwebs partly shown)

V

PRPA

M

C

PP

T

Visual features

C – Cardinal concept nodeM – MemoriesPA – Primary auditoryPP – Phonological productionPR – Phonological recognitionT – TactileV – Visual

Ignition of a functional web from visual input

V

PR

PA

M

C

Art

T

V

PR

PA

M

C

Art

T


Speaking as a response to ignition of a web

V

PR

PA

M

C

Art

T

Speaking as a response to ignition of a web

V

PR

PA

M

C

Art

T

From here (via subcortical structures) to the muscles that control the organs of articulation

An MEG study from Max Planck Institute

Levelt, Praamstra, Meyer, Helenius & Salmelin, J.Cog.Neuroscience 1998

Topics


Hypothesis 2: Nodes as Cortical Columns

• Nodes are implemented as cortical columns• The interconnections are represented by inter-columnar neural

connections and synapses– Axonal fibers – neural output– Dendritic fibers – neural input

The node as a cortical column

• The properties of the cortical column are approximately those described by Vernon Mountcastle – Mountcastle, Perceptual Neuroscience, 1998

• Additional properties of columns and functional webs can be derived from Mountcastle’s treatment together with neurolinguistic findings

Quote from Mountcastle

“[T]he effective unit of operation…is not the single neuron and its axon, but bundles or groups of cells and their axons with similar functional properties and anatomical connections.”

Vernon Mountcastle, Perceptual Neuroscience (1998), p. 192

Three views of the gray matter

Different stains show different features

Layers of the Cortex

From top to bottom, about 3 mm

The Cerebral Cortex

Grey matter• Columns of neurons

White matter • Inter-column connections

Microelectrode penetrations in the paw area of a cat’s cortex

Columns for orientation of lines (visual cortex)

Microelectrode penetrations

K. Obermayer & G.G. Blasdell, 1993

The (Mini)Column

• Width is about (or just larger than) the diameter of a single pyramidal cell– About 30–50 m in diameter

• Extends thru the six cortical layers– Three to six mm in length– The entire thickness of the cortex

is accounted for by the columns • Roughly cylindrical in shape• If expanded by a factor of 100, the

dimensions would correspond to a tube with diameter of 1/8 inch and length of one foot

Simplified model of minicolumn I:Activation of neurons in a column

Thalamus

Other corticallocations

Subcorticallocations

IIIII

IV

VVI

Connections to neighboring columns not shown

Cell Types

Pyramidal

Spiny Stellate

Inhibitory

Cortical column structure

• Minicolumn 30-50 microns diameter• Recurrent axon collaterals of pyramidal

neurons activate other neurons in same column

• Inhibitory neurons can inhibit neurons of neighboring columns– Function: contrast

• Excitatory connections can activate neighboring columns– In this case we get a bundle of

contiguous columns acting as a unit

Cortical minicolumns: Quantities

• Diameter of minicolumn: 30 microns• Neurons per minicolumn: 70-110 (avg. 75-80)• Minicolumns/mm2 of cortical surface: 1460• Minicolumns/cm2 of cortical surface: 146,000• Neurons under 1 sq mm of cortical surface: 110,000• Approximate number of minicolumns in Wernicke’s area:

2,920,000 (at 20 sq cm for Wernicke’s area)

Adapted from Mountcastle 1998: 96

Large-scale cortical anatomy

• The cortex in each hemisphere – Appears to be a three-dimensional structure– But it is actually very thin and very broad

• The grooves – sulci – are there because the cortex is “crumpled” so it will fit inside the skull

Topologically, the cortex of each hemisphere (not including white matter) is..

• Like a thick napkin, with– Area of about 1300 square centimeters

• 200 sq. in.• 2600 sq cm for whole cortex

– Thickness varying from 3 to 5 mm– Subdivided into six layers

• Just looks 3-dimensional because it is “crumpled” so that it will fit inside the skull

Topological essence of cortical structure(known facts from neuroanatomy)

• The thickness of the cortex is entirely accounted for by the columns

• Hence, the cortex is an array of nodes– A two-dimensional structure of

interconnected nodes (columns)• Third dimension for

– Internal structure of the nodes (columns)– Cortico-cortical connections (white matter)

Nodal interconnections (known facts from neuroanatomy)

• Nodes (columns) are connected to– Nearby nodes– Distant nodes

• Connections to nearby nodes are either excitatory or inhibitory – Via horizontal axons (through gray matter)

• Connections to distant nodes are excitatory only– Via long (myelinated) axons of pyramidal neurons

Local and distal connections

excitatory

inhibitory

Simplified model of minicolumn I:Activation of neurons in a column

Thalamus



IIIII

IV

VVI


Cell Types

Pyramidal

Spiny Stellate

Inhibitory

Simplified model of minicolumn II:Inhibition of competitors

Thalamus


IIIII

IV

V

VI

Cells in neighboring columns

Cell Types

Pyramidal

Spiny Stellate

Inhibitory

Local and distal connections

excitatory

inhibitory

Findings relating to columns(Mountcastle, Perceptual Neuroscience, 1998)

• The column is the fundamental module of perceptual systems – probably also of motor systems

• This columnar structure is found in all mammals that have been investigated

• The theory is confirmed by detailed studies of visual, auditory, and somatosensory perception in living cat and monkey brains

Functional webs and subwebs

• A functional web for a word consists of multiple subwebs• Every such subweb

– has a specific function– occupies an area that fits the portion of cortex in

which it located• For example,

– Phonological recognition in Wernicke’s area– Visual subweb in occipital and lower temporal lobe– Tactile subweb in parietal lobe

Hypothesis 3: Nodal Specificity in functional webs

• Every node in a functional web has a specific function• Each node of a subweb also has a specific function

within that of the subweb

Support for Nodal Specificity: the paw area of a cat’s cortex

Column (node) represents specific location on paw

Support for Nodal Specificity:Columns for orientation of lines (visual cortex)

Microelectrode penetrations

K. Obermayer & G.G. Blasdell, 1993

Hypothesis 3a: Adjacency

• Nodes of related function are in adjacent locations– More closely related function, more closely adjacent

• Examples:– Adjacent locations on cat’s paw represented by

adjacent cortical locations– Similar line orientations represented by adjacent

cortical locations

Support for Nodal adjacency: the paw area of a cat’s cortex

Adjacent column in cortex for adjacent location on paw

Hypothesis 4: Extrapolation to Humans

• Hypothesis: The findings about cortical structure and function from experiments on cats, monkeys, and rats can be extrapolated to human cortical structure and function

• In fact, this hypothesis is simply assumed to be valid by neuroscientists

• Why? We know from neuroanatomy that, locally,– Cortical structure is relatively uniform across mammals– Cortical function is relatively uniform across mammals

Hypothesis 4a: Linguistic and conceptual structure

• The extrapolation can be extended to linguistic and conceptual structures and functions

• Why?– Local uniformity of cortical structure and function across

all human cortical areas except for primary areas• Primary visual and primary auditory are known to

have specialized structures, across mammals• Higher level areas are – locally – highly uniform

Conceptual systems and perceptual systems

• Likewise, conceptual systems in humans evidently use the same structures as perceptual systems

• Therefore it is not too great a stretch to suppose that experimental findings on the structure of perceptual systems in monkeys can be applied to an understanding of the structure of conceptual systems of human beings

• In particular to the structures of conceptual categories

Extrapolation to Language?

• Our knowledge of cortical columns comes mostly from studies of perception in cats, monkeys, and rats

• Such studies haven’t been done for language– Cats and monkeys don’t have language– That kind of neurosurgical experiment isn’t done on human

beings• Are they relevant to language anyway?

– Relevant if language uses similar cortical structures– Relevant if linguistic functions are like perceptual functions

Objection

• Cats and monkeys don’t have language• Therefore language must have unique properties of its

structural representation in the cortex• Answer: Yes, language is different, but

– The differences are a consequence not of different (local) structure but differences of connectivity

– The network does not have different kinds of structure for different kinds of information

• Rather, different connectivities

Summary of the argument

• Cortical structure and function, locally, are essentially the same in humans as in cats and monkeys

• Moreover, in humans,– The regions that support language have the same

structure locally as other cortical regions

Support for the connectionist claim

• Lines and nodes (i.e., columns) are approximately the same all over

• Uniformity of cortical structure– Same kinds of columnar structure– Same kinds of neurons– Same kinds of connections

• Conclusion: Different areas have different functions because of what they are connected to

Uniformity of cortical function

• Claims:– Locally, all cortical processing is the same– The apparent differences of function are consequences

of differences in larger-scale connectivity• Conclusion (if the claim is supported):

– Understanding language, even at higher levels, is basically a perceptual process

Hypothesis 5: Hierarchy in functional webs

• A functional web is hierarchically organized

– Bottom levels in primary areas– Lower levels closer to primary areas– Higher (more abstract) levels in

• Associative areas – e.g., angular gyrus• Executive areas – prefrontal• These higher areas are much larger in humans than

in other mammals• Corollary: Each subweb is likewise hierarchically organized

Properties of Hierarchy

• Each level has fewer nodes than lower levels, more than higher levels– Compare the organization of

management of a corporation• Top level has just one node

– Compare the “CEO”

Hypothesis 6: Cardinal nodes

• Every functional web has a cardinal node – At the top of the entire functional web– Unique to that concept– For example, C/cat/ at “top” of the web for CAT

• Corollary: – Each subweb likewise has a cardinal node

• At the top level of the subweb• Unique to that subweb• For example, V/cat/

– At the top of the visual subweb

Cardinal nodes of a functional webSome of the cortical structure relating to dog

V

MC

T

P

PA

PP

Cardinal node of the whole web

Cardinal node of the visual subweb

Each node shown here is the cardinal node of a subweb

Support for the cardinal node hypothesis

1. It follows from the hypotheses of nodal specificity and hierarchy

– A hierarchy must have a highest level– The node at this level must have a specific function

2. It is needed to account for the arbitrariness of the linguistics sign

3. It is automatically recruited in learning anyway, according to the Hebbian learning hypothesis

Cardinal nodes and the linguistic sign

• Connection of conceptual to phonological representation• Consider two possibilities

1. A cardinal node for the concept connected to a cardinal node for the phonological image

2. No cardinal nodes: multiple connections between concept representation and phonological image • supported by Pulvermüller (2002)

Implications of possibility 2

• No cardinal nodes: multiple connections between concept representation and phonological image

• I.e., different parts of meaning connected to different parts of phonological image

• Consider fork– Maybe /f-/ connects to the shape?– Maybe /-or-/ connects to the feeling of holding

a fork in the hand?– Maybe /-k/ connects to the knowledge that

fork is related to knife?• Conclusion: Possibility 2 must be rejected

Topics


Cortical columns do not store symbols

• They only– Receive activation– Maintain activation– Inhibit competitors– Transmit activation

• Important consequence:– We have linguistic information represented

in the cortex without the use of symbols– It’s all in the connectivity

• Challenge:– How?

Columnar Functions: Integration and Broadcasting

• Integration: A column is activated if it receives enough activation from – Other columns – Thalamus

• Can be activated to varying degrees• Can keep activation alive for a period of time• Broadcasting: An activated column transmits activation to

other columns– Exitatory– Inhibitory

• Learning : adjustment of connection strengths and thresholds

Integration and Broadcasting

Broadcasting• To multiple

locations• In parallel

Integration

Integration and Broadcasting

Integration

Broadcasting

Wow, I got activated!

Now I’ll tell my friends!

Processing in the cortex

• Parallel (distributed) and serial• Hierarchical• Bidirectional• Variable

– Varying strengths of connections– Varying degrees of activation– Variation over time

• Adaptability• Learning• Plasticity

Uniformity of structure and function

• Locally,– All cognitive and perceptual information, of any kind,

is represented as nodes and their interconnections– All cognitive processing, of any kind, consists of

broadcasting and integration

Complexity from simplicity

• Complexity: what the brain can do• Simplicity: every node is a simple processor

– Integration– Broadcasting – Changes in connection strengths and thresholds

• Problem: how can such simplicity produce such complexity?• Answer:

– Huge quantity of nodes and connections– Parallel distributed processing– Hierarchical organization

Topics


Additional operations: Learning

• Links get stronger when they are successfully used (Hebbian learning)– Learning consists of strengthening them – Hebb 1948

• Threshold adjustment– When a node is recruited its threshold increases– Otherwise, nodes would be too easily satisfied

Requirements that must be assumed(implied by the Hebbian learning principle)

• Links get stronger when they are successfully used (Hebbian learning)– Learning consists of strengthening them

• Prerequisites: – Initially, connection strengths are very weak

• Term: Latent Links– They must be accompanied by nodes

• Term: Latent Nodes– Latent nodes and latent connections must be available for learning

anything learnable• The Abundance Hypothesis

– Abundant latent links – Abundant latent nodes

Support for the abundance hypothesis

• Abundance is a property of biological systems generally– Cf.: Acorns falling from an oak tree– Cf.: A sea tortoise lays thousands of eggs

• Only a few will produce viable offspring– Cf. Edelman: “silent synapses”

• The great preponderance of cortical synapses are “silent” (i.e., latent)

– Electrical activity sent from a cell body to its axon travels to thousands of axon branches, even though only one or a few of them may lead to downstream activation

Locations of available latent connections

• Local – Surrounding area– Horizontal connections (not white matter)

• Intermediate– Short-distance fibers in white matter– For example from one gyrus to neighboring gyrus

• Long-distance– Long-distance fiber bundles– At ends, considerable branching

Learning – The Basic Process

Latent nodes

Latent links

Dedicated nodes and links

Latent nodes

Let these links get activated



Latent nodes

Then these nodes will get activated


That will activate these links

Learning – The Basic Process This node gets enough activation to satisfy its threshold


These links now get strengthened and the node’s threshold gets raised A

B

This node is therefore recruited

Learning – The Basic ProcessThis node is now dedicated to function AB

AB

AB

LearningNext time it gets activated it will send activation on these links to next level

AB

AB

Learning: Deductions from the basic process

• Learning is generally bottom-up. • The knowledge structure as learned by the cognitive

network is hierarchical — has multiple layers• Hierarchy and proximity:

– Logically adjacent levels in a hierarchy can be expected to be locally adjacent

• Excitatory connections are predominantly from one layer of a hierarchy to the next

• Higher levels will tend to have larger numbers of nodes than lower levels

Learning in cortical networks:A Darwinian process

• It works by trial-and-error – Thousands of possibilities available

• The abundance hypothesis– Strengthen those few that succeed

• “Neural Darwinism” (Edelman)• The abundance hypothesis

– Needed to allow flexibility of learning– Abundant latent nodes

• Must be present throughout cortex– Abundant latent connections of a node

• Every node must have abundant latent links

Learning – Enhanced understanding

• This “basic process” is not the full story• The nodes of this depiction:

– Are they minicolumns, maxicolumns, or what?– Nodes of the model may be represented by

• Minicolumns or• Contiguous bundles of minicolumns

– Of different sizes» “maxicolumns”, “hypercolumns”

Findings of Mountcastle:Columns of different sizes for categories and subcategories

• Minicolumn– The smallest unit– 70-110 neurons

• Functional column– Variable size – depends on experience– Intermediate between minicolumn and maxicolumn

• Maxicolumn (a.k.a. column)– 100 to a few hundred minicolumns

• Hypercolumn– Several contiguous maxicolumns

Hypercolums: Modules of maxicolumns

A visual area in temporal lobe of a macaque monkey

Perceptual subcategories andcolumnar subdivisions of larger columns

• Nodal specificity applies for maxicolumns as well as for minicolumns

• The adjacency hypothesis likewise applies to larger categories and columns– Adjacency applies for adjacent maxicolumns

• Subcategories of a category have similar function– Therefore their cardinal nodes should be in

adjacent locations

Functional columns

• The minicolumns within a maxicolumn respond to a common set of features

• Functional columns are intermediate in size between minicolumns and maxicolumns

• Different functional columns within a maxicolumn are distinct because of non-shared additional features – Shared within the functional column– Not shared with the rest of the maxicolumn

Mountcastle: “The neurons of a [maxi]column have certain sets of static and dynamic properties in common, upon which others that may differ are superimposed.”

Similarly..

• Neurons of a hypercolumn may have similar response features, upon which others that differ may be superimposed

• Result is maxicolumns in the hypercolumn sharing certain basic features while differing with respect to others

• Such maxicolumns may be further subdivided into functional columns on the basis of additional features

• That is, columnar structure directly maps categories and subcategories

(!)

Hypercolumns: Modules of maxicolumns

A visual area in the temporal lobe of a macaque monkey

Category (hypercolumn)

Subcategory(can be further subdivided)

Learning in a system with columns of different sizes

• At early learning stage, maybe a whole hypercolumn gets recruited

• Later, subdivided into maxicolumns for further distinctions• Still later, functional columns as subcolumns within

maxicolumns• New term: Supercolumn – a group of minicolumns of whatever

size, hypercolumn, maxicolumn, functional column• Links between supercolumns will thus consist of multiple fibers

Latent super-columns

Bundles of latent links

Dedicated super-columns and links

Revisit the diagram: Each node of the diagram represents a group of minicolumns – a supercolumn

Let these links get activated


Learning – The Basic Process:Refined view

Then these supercolumns get activated

Learning – The Basic Process:Refined view

That will activate these links

Learning – Refined view This supercolumn gets enough activation to satisfy its threshold

Learning – Refined viewThis super-column is recruited for function AB

AB

AB

Learning:Refined view

Next time it gets activated it will send activation on these links to next level

AB

AB

LearningRefined view

Can get subdivided for finer distinctions

AB

AB

A further enhancement

• Minicolumns within a supercolumn have mutual horizontal excitatory connections

• Therefore, some minicolumns can get activated from their neighbors even if they don’t receive activation from outside

Learning: Refined view

Hypercolumn composed of 3 maxicolumns Can get subdivided for finer distinctions

AB

AB

Learning: refined viewIf, later, C is activated along with A and B, then maxicolumn ABC is recruited for ABC

AB

AB

C

ABC

Learning: refined view

And the connection from C to ABC is strengthened –it is no longer latent

AB

AB

C

ABC

Topics


T h a n k y o u f o r y o u r a t t e n t I o n !

ReferencesLamb, Sydney, 1999. Pathways of the Brain: The Neurocognitive Basis of Language. John

Benjamins.Mountcastle, Vernon, 1998. Perceptual

Neuroscience: The Cerebral Cortex. Harvard University Press.Pulvermüller, Friedemann, 2002. The

Neuroscience of Language. Cambridge University Press

Internet Sources

www.rice.edu/langbrain

www.owlnet.rice.edu/ling411/ClassNotes

http://www.rice.edu/langbrain

http://www.owlnet.rice.edu/ling411/ClassNotes

For further information..

www.rice.edu/langbrain

[email protected]

http://www.rice.edu/langbrain

The two big problems of neurosyntaxHow does the brain handle..

1. Sequencing – ordering of words in a sentence– And ordering of phonemes in a word

2. Categories– Noun, Verb, Preposition, etc.

• Subtypes of nouns, verbs, etc.– What categories are actually used in syntax?– How are syntactic categories defined?– How represented in the brain?– How does a child build up knowledge of such categories

based on just his/her ordinary language experience?

First step: accounting for sequence

• Important not just for language– Dancing– Eating a meal– Events of the day, of the year, etc.– Etc., etc.

• In language, not just syntax (lexotactics)– Ordering of morphemes in a word

• Morphotactics – Order of phonological elements in syllables

• Phonotactics

Neurological Structures for Sequence

• How is sequencing implemented in neural structure?

• For an answer, consider the structure of the cortical column

Lasting activation in minicolumn



Cell Types

Pyramidal

Spiny Stellate

Inhibitory

Recurrent axon branches keep activation alive in the column –Until is is turned off by inhibitory cell

The ‘Wait’ Element

W

1

2

www.ruf.rice.edu/~lngbrain/neel

http://www.ruf.rice.edu/~lngbrain/neel

Lasting activation in minicolumn



Cell Types

Pyramidal

Spiny Stellate

Inhibitory

Recurrent axon branches keep activation alive in the column –Until is is turned off by inhibitory cell

Simple notation for lasting activation

Thick border for a node that stays active for a relatively long time Thin border for a node

that stays active for a relatively short time

N.B.: Nodes are implemented as cortical columns

Recognizing items in sequence

This link stays active

a b

Node c is satisfied by activation from both a and b If satisfied it sends activation to output connections Node a keeps itself active for a whileSuppose that node b is activated after node a Then c will recognize the sequence ab

c

This node recognizes the sequence ab

Example: eat apple(structure for recognition)

eat apple

eat apple

(Just labels, not part of the structure)

Example: eat apple, eat banana(structure for recognition)

eat apple eat banana

eat apple banana

Producing items in sequence

ab

a b

Wait element

First a, then b

How does the delay element work?

• Remember: each node is implemented as a cortical column– Within the column are 75-110 neurons

• Enough for considerable internal structure• When node ab receives activation, it

– Sends activation on down to node a– And to the delay element, which

• Waits for activation from clock timer or feedback– Will come in on line labeled ‘f’ in diagram

• Upon receiving this signal, sends activation on to node b


ab

a b

Delay element

Carries feedback or clock signal

f


ab

a b

May be within one cortical column

f

Producing items in sequencea different means

a b

f

This would apply for items ‘a’ and ‘b’ in sequence where there is no ‘ab’ to be recognized as a unit.Example: Adjectives of size precede adjectives of color, which precede adjectives of material in the English noun phrase, as in big brown wooden box

Two different network notations

Narrow notation• Nodes represent cortical columns• Links represent neural fibers• Uni-directional• Close to neurological structure

Abstract notation• Nodes show type of relationship (OR,

AND)• Easier for representing linguistic

relationships• Bidirectional • Not as close to neurological structure

eat apple

eat apple

eat apple

eat apple

Two different network notationsNarrow notation

ab

a b

b

a b

Abstract notation Bidirectional

ab

a b f

Upward Downward

Constructions have meanings and functions

• They are also signs

Meaning/Function

Form/Expression

The sign relationship: a (neural) connection

The difference is that for a construction the expression is variable rather than fixed

The transitive verb phrase construction

CLAUSE DO-TO-SMTHG

Vt NP

Transitive verb phrase

Syntactic function

Semantic function

Variable expression

Linked constructions

CL

NP

DO-TO-SMTHG

Vt NP


The clause construction

Add a few more connections

CL

NP

DO-TO-SMTHG

Vt


ACTOR-DO

Add other types of predicate

CL

DO-TO-SMTHG

THING-DESCR

BE-SMTHG

be

NP

Vt

Adj

Vi

Loc

(A rough first approximation)

The other big problem for syntax

• Categories• Problems of categories are considered in a separate

presentation

on the neurocognitive basis of language sydney lamb l [email protected] 2010 november 12 wenzao ursuline...

Documents

cortexmore operations

wide area of cortexmeaning

functional webspread

nonlinguistic information

functional web pulvermller

functional websa word

persons linguistic

conceptual system