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Ling 411 – 13
Words in the Brain:
Functional Webs
REVIEW
Findings relating to columns
(Mountcastle, Perceptual Neuroscience, 1998)
 The column is the fundamental module of
perceptual systems
• probably also of motor systems
 Perceptual functions are very highly localized
• Each column has a very specific local function
 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
REVIEW
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
REVIEW
Quote from Hjelmslev
The postulation of objects as something different from
the terms of relationships is a superfluous axiom and
consequently a metaphysical hypothesis from which
linguistic science will have to be freed.
Louis Hjelmslev
Prolegomena to a Theory of Language
(1943: 61)
Columnar Functions:
Integration and Broadcasting
REVIEW
 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
REVIEW
What matters is not ‘what’ but ‘where’
 What distinguishes one kind of information from
another is what it is connected to
 Lines and nodes are approximately the same all over
 Hence, uniformity of cortical structure
• Same kinds of columnar structure
• Same kinds of neurons
• Same kinds of connections
 Different areas have different functions because of
what they are connected to
REVIEW
Operations in relational networks
 Activation moves along lines and through nodes
• Integration
• Broadcasting
 Connection strengths are variable
• A connection becomes stronger with repeated
successful use
• A stronger connection can carry greater activation
REVIEW
Operation of the Network
 The linguistic system operates as distributed
processing of multiple individual components –
cortical columns
 Columnar Functions
• Integration: A column is activated if it receives
enough activation from other columns
 Can be activated to varying degrees
 Can keep activation alive for a period of time
• Broadcasting: An activated column transmits
activation to other columns
 Excitatory – contribution to higher level
 Inhibitory – dampens competition at same level
 Columns do not store symbols
Functional webs as neural basis of cognition
 Earlier proposals (Pulvermüller 2002: p. 23)
• Individual neurons (Barlow 1972)
 Individual neurons too noisy and unreliable
 Would require more information processing
capacity than one neuron has
• Mass activity and interference patterns in the
entire cortex (Lashley 1950)
 Better alternative:
• Functional webs of neurons (Pulvermüller)
 Even better
• Functional webs of cortical columns
• (not mentioned by Pulvermüller)
Pulvermüller’s functional webs
 A large set of neurons that
• Are strongly connected to each other
• Are distributed over a set of cortical areas
• Work together as a functional unit
• Are functionally interdependent so that each is
necessary for the optimal functioning of the web
(2002: 24)
Deductions from findings about cortical columns
 If linguistic structure is purely relational, then the
properties of cortical structure identified earlier also
apply to language
• So they also apply to functional webs
 A functional web is a subnetwork of the linguistic network






• Consisting of nodes and their interconnections
Property I: Intra-column uniformity of function
Property II: Cortical topography
Property III: Nodal specificity
Property IV: Adjacency
Property V: Extension of II-IV to larger columns
Property VI: Competition
Deductions from findings about cortical columns
 If linguistic structure is purely relational, then the
properties of cortical structure identified earlier
also apply to language
• So they also apply to functional webs
 Property I: Intra-column uniformity of function
• Therefore, the nodes of functional webs are
(implemented as) cortical columns
Deductions: Properties of Functional Webs
 If linguistic structure is purely relational, as seems
likely, then the properties of cortical structure
identified earlier also apply to language
• So they also apply to functional webs
 Property I: Intra-column uniformity of function
• Therefore, the nodes of functional webs are
(implemented as) cortical columns
 Property II: Cortical topography
• Linguistic structure as a two-dimensional array
of nodes
• Therefore, every functional web is a twodimensional array of columns
Deductions: Properties of Functional Webs




Properties of cortical structure applied to language:
Property I: Intra-column uniformity of function
Property II: Cortical topography
Property III: Nodal specificity
• Every linguistic node has a specific function
• So every node of a functional web has a specific
function
• This point represents a disagreement with
Pulvermüller’s view
 Property IV: Adjacency
 Property V: Extension of II-IV to larger columns
 Property VI: Competition
Support for Nodal Specificity: the paw
area of a cat’s cortex
Column (node) represents
specific location on paw
REVIEW
Pulvermüller’s functional webs
 For example, a web for the word ‘cat’
 Pulvermüller:
• A significant portion of the web’s neurons are
active whenever the cat concept is being processed
• The function of the web depends on the intactness
of its member neurons
• If neurons in the functional web are strongly linked,
they should show similar response properties in
neurophysiological experiments
(2002:26)
A Memory Experiment
(Pulverműller 2002: 26-27)
 Performed with macaque monkeys
 Delayed matching – monkey must remember
• Monkey must keep in mind the shape or color of
an object and perform a matching response after
delay of several seconds
 Neural activity detected in frontal and temporal lobes
 Temporary lesion of frontal or temporal area leads to
impaired stimulus specificity in other area
 Supports the hypothesis of a functional web including
sites in frontal and temporal areas
Pulvermüller’s line of reasoning
1.
2.
3.
“If neurons in the functional web are strongly linked, they
should show similar response properties in
neurophysiological experiments.
“If the neurons of the functional web are necessary for
the optimal processing of the represented entity, lesion
of a significant portion of the network neurons must
impair the processing of this entity. This should be largely
independent of where in the network the lesion occurs.
“Therefore, if the functional web is distributed over
distant cortical areas, for instance, certain frontal and
temporal areas, neurons in both areas should (i) share
specific response features and (ii) show these response
features only if the respective other area is intact.”
(2002: 26, see also 27)
Reasoning from memory experiment
 Temporary lesion of frontal or temporal area leads
to impaired stimulus specificity in other area
 “Together, these data provide evidence that
neurons in both temporal and frontal areas (a)
showed the same specific response features and
(b) showed these response features if and only if
the respective other area was intact…”
 Compares language impairment vis-à-vis
Wernicke’s and Broca’s areas (2002: 28)
Not so fast!
… the same specific response features?
Elsewhere he writes “similar”
“If neurons in the functional web are strongly linked,
they should show similar response properties in
neurophysiological experiments.”
(2002:26)
N.B.: similar – not same!
 Similar:
•
•
Sharing some features
There may be differences with respect to other
features
Pulvermüller’s reasoning (cont’d)
“These results obtained in memory experiments with
macaque monkeys are reminiscent of well-known facts
from … investigation into acquired language disorders … .
These … studies … showed that prefrontal and temporal
areas are most crucial for language processing. They also
showed that lesions in either area can lead to aphasia,
which in the majority of cases include deficits in both
language production … and perception … .”
(2002: 28)
Pulvermüller on Wernicke’s aphasia
“… patients with Wernicke’s aphasia have difficulty
speaking…. These deficits are typical…and cannot be
easily explained by assuming a selective lesion to a
center devoted to language comprehension.”
(2002: 36-37)
Pulvermüller’s hypothesis on
phonological word forms
“The functional webs realizing
phonological word forms may
be distributed over the
perisylvian area of the
dominant left hemishpere.
Circles represent local neuron
clusters and lines represent
reciprocal connections
between them.”
Friedemann Pulvermüller, The Neuroscience of Language, 2002: 52
REVIEW
Basic and complex functions
 Phonological recognition is a basic function
• Located in Wernicke’s area
 Speaking is a complex function
• A cooperative effort of several areas, including
Broca’s area and Wernicke’s area
• Phonological recognition is a necessary component of
speaking
Wernicke:
“Primary functions alone can be referred to specific areas…. All
processes which exceed these primary functions…are dependent
on the fiber bundles, that is, association.”
Aphasia Symptom Complex (1874)
REVIEW
Wernicke’s Area and Speaking
 Phonological images guide speech production
 Phonological recognition monitors production
 Compare..
• Painting without visual perception
• Playing a piano without auditory perception
 Conclusion: Of course phonological recognition (i.e.
Wernicke’s area) plays a role in speech production
REVIEW
Paraphrasing Pulvermüller
…patients with Wernicke’s aphasia have difficulty
speaking…. These deficits are typical…and cannot be easily
explained by assuming a selective lesion to a center
devoted to language comprehension.
The Neuroscience of Language (2002)
Altered quote:
…patients with damage to the occipital lobe have
difficulty drawing pictures…. These deficits are
typical…and cannot be easily explained by assuming a
selective lesion to a center devoted to visual perception.
Re-examining the monkey memory experiment
(and revising Pulvermüller’s conclusion)
 Compare short-term verbal memory
• Hypothesis: reverberating activation between
Broca’s area and Wernicke’s area
• If one of those areas is impaired, the
reverberating activity is disrupted, leading to
diminished activity in the other area
 Same principle could apply in memory test
in macaque monkey
• Reverberation between temporal lobe
(recognition zone) and frontal lobe (action zone)
 Does not require that the two areas share
“same specific response features”
Conclusion:
The components of a functional web are diverse
 The phonological representation of a word may be seen as a
functional web in the perisylvian area
 But each component of the web has its own specific local
function within that representation
• For example, phonological recognition in Wernicke’s area
 If they are all the same, why have many of them, spread out
over different areas?
Compare Property III: Nodal specificity
Deductions: Properties of Functional Webs




Properties of cortical structure applied to language:
Property I: Intra-column uniformity of function
Property II: Cortical topography
Property III: Nodal specificity
• Every linguistic node has a specific function
• So every node of a functional web has a specific
function
• This point represents a disagreement with
Pulvermüller’s view
 Property IV: Adjacency
 Property V: Extension of II-IV to larger columns
 Property VI: Competition
Elsewhere, Pulvermüller gets it right
“…activation of the web, so to speak, completes itself as a
result of the strong web-internal links. If the web of
neurons is considered a memory representation of an
object and each neuron to represent one particular
feature of this object memory, the full ignition would be
the neuronal correlate of the activation of the stored
object representation. Such full activation of the object
memory could occur if only a fraction of the features of
the object are present in the actual input.” (2002: 29)
Why do the nodes in a web appear to have
similar response features?
 Not because each node has – on its own – response
features similar to those of other nodes in the web
 Simply because all the nodes are “tied together” in
the web
• Therefore, all respond when the whole web is
ignited
 Actually they have, individually, very different
response features
• E.g. in Wernicke’s area and in Broca’s area
Localizing components of Functional Webs

A functional web is spread over a wide area of cortex
• Includes perceptual information

Relating to the meaning
• Visual: occipital and temporal
• Auditory: temporal
• Somatosensory: parietal
• As well as phonological information

•
Temporal, parietal, frontal
As well as specifically conceptual information
• For nominal concepts, mainly in
• Angular gyrus and/or middle temporal gyrus and/or
•
BA 37
(?) Maybe also supramarginal gyrus
Deductions: Properties of Functional Webs





Properties of cortical structure applied to language:
Property I: Intra-column uniformity of function
Property II: Cortical topography
Property III: Nodal specificity
Property IV: Adjacency
• Adjacent linguistic nodes have similar linguistic functions
• Therefore, in functional webs, nodes of related function
are in adjacent locations
• And, more closely related function, more closely adjacent
Property IV(b): A deduction from the adjacency property
 The nodes in each area of a functional web
• Constitute a subweb
• Their function fits the portion of cortex in which
they are located
 For example,
• Phonological recognition in Wernicke’s area
• Visual subweb in occipital and lower temporal lobe
• Tactile subweb in parietal lobe
• Nodal specificity: Each node of a subweb also has
a specific function within that of the subweb
Property IV(c): Functional specificity of subwebs
 The nodes in each area of a functional web
• Constitute a subweb
• Each node of a subweb has a specific function
within that of the subweb (Property III)
• Each subweb has specific function within the web
 Fits its location in the cortex
 For example,
• Visual subweb in occipital and lower temporal lobe
• Tactile subweb in parietal lobe
Example: The meaning of 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
A phonological subweb: /bil/
bil
Cardinal node for bill
Subweb for bill
bi-
-il
A functional web showing two subwebs
T
C
PP
PR
PA
M
Control of articulation
V
Visual features
Deductions: Properties of Functional Webs
 If linguistic structure is purely relational, as seems
likely, then the properties of cortical structure
identified earlier also apply to language:
 Property I: Intra-column uniformity of function
 Property II: Cortical topography
 Property III: Nodal specificity
 Property IV: Adjacency
 Property V: Competition
• Contiguous linguistic nodes are in competition
 E.g. , stop consonants
 Property VI: Extension of II-IV to larger columns
Deductions: Properties of Functional Webs
 If linguistic structure is purely relational, as seems
likely, then the properties of cortical structure
identified earlier also apply to language:
 Property I: Intra-column uniformity of function
 Property II: Cortical topography
 Property III: Nodal specificity
 Property IV: Adjacency
 Property V: Competition
 Property VI: Extension of II-IV to larger columns
• Linguistic categories in neighboring cortical areas
• (to be considered later)
Three more properties
 Property VII: Hierarchy in functional webs
 Property VIII: Cardinal nodes
 Property IX: Reverberation
Property VII: 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
 Property VII(a): Each subweb is likewise
hierarchically organized
Hierarchy in a visual subweb
A network of
visual features
V
FORK
Etc. etc.
(many layers)
Properties of Hierarchy
 Relates to general hierarchy in the cortex
 Each level has fewer nodes than lower
levels, more than higher levels
• Compare
 The organization of management
of a corporation
 Ranks in an army or navy
Property VIII: 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
 Property VIII(a):
• 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
(Part of) the functional web for the
concept CAT
The cardinal node for the
entire functional web
T
C
P
A
M
V
Cardinal nodes
of subwebs
The Wernicke-Lichtheim concept node (1885)
Where?
The “C” Node
 Not just in one place
• Conceptual information for a single word
is widely distributed
• Conceptual information is in different
areas for different kinds of concepts
 The second of these points and probably also
the first were already recognized by Wernicke
 But..
• There may be a single “C” node anyway as
cardinal node of a distributed network
“C” node as cardinal node of a web
For example, FORK
T
C
M
V
Labels for Properties:
C – Conceptual
M – Motor
T – Tactile
V - Visual
Each node in this diagram
represents the cardinal node
of a subweb of properties
Some connections of the “C” node for FORK
Each node in this diagram
represents the cardinal node
of a subweb of properties
T
For example,
C
M
V
Let’s
zoom in
on this
one
Zooming in on the “V” Node..
A network of
visual features
V
FORK
Etc. etc.
(many layers)
Add phonological recognition node
For example, FORK
C
T
M
P
V
Labels for Properties:
C – Conceptual
M – Motor
P – Phonological image
T – Tactile
V – Visual
The phonological image
of the spoken form [fork]
(in Wernicke’s area)
Add node in primary auditory area
For example, FORK
C
T
M
P
PA
V
Labels for Properties:
C – Conceptual
M – Motor
P – Phonological image
PA – Primary Auditory
T – Tactile
V – Visual
Primary Auditory: the cortical structures in the primary
auditory cortex that are activated when the ears receive
the vibrations of the spoken form [fork]
Add node for phonological production
For example, FORK
C
T
M
P
PP
PA
V
Arcuate fasciculus
Articulatory structures (in Broca’s
area) that control articulation of
the spoken form [fork]
Labels for Properties:
C – Conceptual
M – Motor
P – Phonological image
PA – Primary Auditory
PP – Phonological Production
T – Tactile
V – Visual
Some of the cortical structure relating to fork
(showing cardinal nodes only)
T
M
PP
C
P
PA
V
Functional web of a simple lexeme: fork
Meaning
Phonological
form
T
M
PP
C
P
PA
V
Link
between
form and
meaning
A functional web with two subwebs partly shown
T
C
PP
PR
PA
M
C – Cardinal concept node
M – Memories
PA – Primary auditory
PP – Phonological production
PR – Phonological recognition
T – Tactile
V – Visual
V
Visual features
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Ignition of a functional web from visual input
T
C
PR
Art
PA
M
V
Speaking as a response to ignition of a web
T
C
PR
Art
PA
M
V
Speaking as a response to ignition of a web
T
C
PR
Art
PA
M
V
Speaking as a response to ignition of a web
T
C
PR
Art
PA
M
From here (via subcortical
structures) to the muscles that
control the organs of articulation
V
An MEG study from Max Planck Institute
The argument against cardinal nodes
 Pulvermüller: “It is not necessary to
assume a cardinal node” (p. 24)
 Arguments by others (directed against
“grandmother nodes”):
• Not enough flexibility
• Not enough availability
 Response to the arguments:
• The cardinal node of a hierarchical web is not
a “grandmother node” as usually understood
• It is supported by the hierarchy principle
• Compare
 CEO of a corporation
 President of the U.S.
The “Grandmother Node”
(Cardinal node for your grandmother)
 Grandmother node
• A node that represents “grandmother”
 An untenable hypothesis, according to the usual
conception
 But two separate conceptions to be distinguished
• A node that represents “grandmother” all by itself
• A node whose receptive field is “grandmother”
The untenable grandmother node
 A node that would recognize grandmother all by itself
• Such a node would have to be extraordinarily complex
 How could one node recognize grandmother
• In different positions/postures
• In different clothing
• At different ages
• Criticisms of such a conception are well-founded
 Such a hypothesis involves local representation without
distributed representation
A sophisticated grandmother node
 GRANDMOTHER has a distributed representation
 It also has a cardinal node (local representation)
• A ‘grandmother node’ in the sophisticated sense
• It represents a specific value: GRANDMOTHER
• Its receptive field is “grandmother”
 It works because it is the cardinal node of an entire
functional web
• Other nodes in the web handle
 The details
 A range of diverse perceptual properties
Arguments against ‘grandmother nodes’
 They usually assume that the local representation is
representing a concept (like ‘grandmother’) all by itself
• i.e., Local representation without distributed
representation
 i.e., without a supporting web
to be continued . . .
end