Lexical Semantic

8/2/2019 Lexical Semantic

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Lexical semantics


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What is meaning and how is it linked toword forms and to larger linguisticunits?

Word semantics Prototype theory

Semantic distinctive features

Semantic fields

Semantic features and operations in aphasia

Sources of data and theories

Deep dyslexia

Category-specific anomia

Right-hemisphere lesions and lexical-semanticproblems

Semantic dementia

Methodological considerations

Group studies versus case studies

Central or access disorder

Mapping of form and meaning

Types of process models

Word comprehension

Word production

Simulation

Links to therapy


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Nominalism

there are objects and phenomena in theworld and words to denote them; nothingelse (i.e., no intermediate representation) isneeded.

Conceptualism (most often found in

neurolinguistic studies):

there are concepts in our minds that linkwords to objects and phenomena in theworld.

Conceptual realism

concepts exist in themselves,independently of human minds (e.g., so-called Platonic ideas).


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Basic units of meaning

What is or can be the basic units ofmeaning?

words, parts of words, or evensmaller features

sentences, utterances, contributions,

longer texts, monologues, ordialogues

Or could they all be?

And what is the relationship between

the meanings of linguistic units andtheir context of use?


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Anomia

Anomia (difficulties in findingcontent words) is a symptomshared by almost all persons withaphasia.

(In the type of aphasia called

anomic aphasia, this is the onlysymptom; while in the other types ofaphasia, it is one of severalsymptoms.)

Anomia creates problems in taskssuch as naming objects (visuallydisplayed, from verbal descriptions,or from memory).


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Hypotheses about themental lexicon

Aphasic ways of searching for words andaphasic semantic word substitutions(semantic paraphasias) have been used totest different hypotheses about how amental lexicon can be organized.

Central or access disorder?

A basic question is whether the lexiconcan be disturbed in itself that is, can itsorganization be affected? or whetheronly the ways of accessing the lexicon canbe disturbed.

Since we are dealing with patterns ofactivation in the brain, this is really apseudo-question, or rather a questionregarding the quality, degree, or variationin activation patterns


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Example

Target word: LADDERA: yes there we have it there he had

one of those yesterday the one whopicked apples I know so well whatits called we have one over there by

the shed no cannotTarget word: SHOEMAKER

A: carpen no it isnt that shoebake shoebaker, no carpen carpen

T: shoemake A: shoebaker

T: no shoemake

P: shoemaker


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Prototype theory

Rosch (1975) Categories are organized around the

most prototypical exemplars, which

are central and more stable.

prototypical items, are namedmore easily and consistently than

more atypical exemplars,

exemplars that are borderline

between categories are associated

with the fuzzy fringes of the fields.


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Prototype theory andaphasia

Prototype theory Whitehouse, Caramazza, and Zurif (1978)(in an experiment designed by Labov,1973).

The task was to determine whether drawnobjects were cups, plates, or glasses.

Stimuli gradually became more similar andit was noted where each person drew thelimits between the different types ofobjects.

Brocas aphasics used the same strategies

as controls for classifying objects Anomic aphasics either showed a total

inability to name objects systematically orused rules that were too simple. They werealso unable to use the added context in apicture as a cue.


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Superordinate-Basic-Subordinate level

Prototype theory has been combinedwith considerations of differentlevels of abstraction in a hierarchicalorganization of semantic categoriesinto

- superordinate (animal)- basic (dog)

- subordinate (poodle)

levels.

It has been claimed that base-levelwords are more likely to beprototypical, and remain morerobust for many persons withaphasia


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Therapy effects

Studies by Kiran and colleagueshave shown that there is a

semantic complexity effect, in

that training on atypical

examples of animate andinanimate categories and their

semantic features leads to

improvement in the naming of

more typical exemplars as well,whereas the reverse does not

hold


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Semantic DistinctiveFeatures

The idea is that a category can beidentified and described withreference to the necessary andsufficient conditions for belongingto that category.

This process therefore involvesdecomposition into more primitiveor basic features.

Examples of semantic distinctivefeatures are

[+living], [+male], [ adult] for boy.


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Semantic features andaphasia

The words the participants had to classifywere mother, wife, cook, partner, knight,husband, shark, trout, dog, tiger, turtle,and crocodile.

The controls tended to classify the words

into the human and animal categories,

Brocas aphasics divided them into human+ dog versus other animals.

Controls then sorted the animals according

to species. Brocas aphasics sorted them into more or

less dangerous groups.


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Controls used semantic features in asystematic, technical way.

Brocas aphasics used temporary andconspicuous features and were more

dependent on emotional andsituational influences.

Wernickes aphasics used

indeterminate and deviant featuresand were generally out of focus.


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Semantic fields ornetworks

Semantic fields or networks aregroupings of words according tosemantic similarity, or contiguity(co-occurrence), relations.

Hierarchical and similarity-based

word association network used byCollins and Quillian (1969), basedon is a relations between words;for example, apoodle is a dog, a dogis an animal.

Especially for natural kinds, this is agood way of describingparadigmatic, similarity-basedrelations.


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Collins and Loftus (1975) model of word meanings based

on semantic similarity.

Words are activated byspreading activation in thenetwork when related words arearoused.

This is the basis for semanticpriming of word recognition

(i.e., that a word is recognizedfaster if it has been preceded bya semantically related word).


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There are, however, alsosyntagmatic semantic field

relations between words, based

on contiguity or co-occurrence.

Such relations exist betweenword pairs such as catand dog,

eatandfood, or redand light.


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Similarity - Contiguity

Similarity and contiguity relationsinteract in determining associationstrength between words.

For example, catand dog bothbelong to the same category in a

hierarchical, similarity-based field, but they also tend to co-occur in

expressions such as cats and dogs.

Semantic fields can be based onrelations between words, which arein turn based on relations betweenobjects, events, and properties in theworld.


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Semantic fields andaphasia

Wernickes aphasics in particularhave difficulties in recognizing and

using the relations.

Luria (1976) claimed that words

have graded semantic associative

fields.

Goodglass and Baker (1976)

- parts of these fields could be

damaged selectively

- object naming was affected by how

much of the semantic field was

accessible.


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Task: to name objects and then judge whetherother words were associated with the

object names

The speed of recognizing associated words

was measured.

All subjects had shorter response times forwords associated with objects that they had

been able to name.

Certain associated words were consistently

easier, while others were harder to

recognize.


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Meaning potential andsemantic operations

Words have meaning potentials andhave their specific meaningdetermined by the current context(Allwood 1999, 2003).

Context determination of meaning is

crucial and lexical semantics worksby semantic operations on meaningpotentials.

Semantics and pragmatics are, thus,unified.

This perspective is also importantwhen looking at communicativecontributions in context


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Semantic features andoperations in Aphasia

An intended target word is very often replaced by aword that is semantically and/or phonologicallyrelated to it.

The semantic relation can be based on similarity orcontiguity (i.e., co-occurrence ).

Some semantic relations that are often found inthese situations are

same semantic category

superordinate

subordinate

part for whole

attribute

spatial relation

functional-causal relation.


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Many semantic substitutions andparaphrases (circumlocutions) describe

situational features, indicating a need to

contextualize.

More substitutions seem to move in thedirection from abstract to concrete than in

the opposite direction, indicating

difficulties with abstraction

(Allwood & Ahlsn, 1986, 1991).


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Same category: catfor dog Superordinate: dog forpoodle

Subordinate:poodle for dog

Part for whole: trunkfor elephant

Attribute:yellow for banana Spatial relation: headfor cap

Functional causal relation: kickforball

Circumlocution: he had one of thoseyesterday, the one who picked appleswe have one over by the shedforladder


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Category-specificAnomia

anomia that affects a certaincategory of words, but leaves

other categories unaffected.


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Nouns vs verbs

Nouns and verbs can be selectivelydisturbed in relation to each other.

Verbs - nonfluent, agrammatic aphasics withfrontal lobe lesions.

Nouns - persons with anomia, who have temporal-

parietal lesions.

The verb disorder can be considered in relation to a

possible frontal encoding of verbs of movement and

action

It may also be related to the role of verbs in

grammatical structure.The noun disorder would be more related to the

association of sensory features.


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Concrete vs abstract

Concreteness effect:

concrete nouns are more easily activated.

Why?

- concrete nouns have richer representationalstructures in memory, including, for example, anonverbal image coding?

- more contextual information?

- a larger set of semantic features?

But some (albeit few) persons with aphasia activateabstract nouns more easily.

Another argument is that concrete nouns arespecifically associated with sensorimotor (includingperceptual) attributes

If these attributes are disturbed, abstract nounswould be easier to access than concrete ones.


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Natural/living objects vs artifacts

Selective disturbances of

- words for either natural objects (animal,fruits, vegetables) or

- artifacts (tools, furniture, etc).Such patients may have very vaguesemantic information about one of thecategory types, but very detailed semanticinformation about the other type.

Why?- mainly perceptual/sensory versus mainlyfunctional/motor basis (for natural objectsand artifacts, respectively)

Support: naming of animals resulted inactivation in the left medial occipital lobe,while naming of tools activated the leftpremotor area.

or

we really have more detailed category-specificity in the organization of our

mental lexicon.


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Semantic word substitutions seem to keepwithin category and resemble speech

errorsmade by normal speakers (e.g., bigbecomes small) (Buckingham, 1979). Others have

studied conceptual organization. Zurif, Caramazza,

Foldi, and Gardner (1979) found that both Brocas

and Wernickes aphasics had difficulties instructuring lexical knowledge by conceptual

features. The subjects first had to sort words

according to thematic relations and common

conceptual features. Then they were given a word

recognition test in order to see whether these

relations were actually used. The words wererelated in the following ways:


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MethodologicalConsiderations

Groups studies vs case studies Central or access disorder


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Mapping of Form and Meaning

How words are processed - how form andmeaning are mapped onto each other inlanguage production and comprehension.

in relation to process models of differenttypes and to the units studied,

How much top-down versus bottom-upprocessing is assumed to take place?

When we understand speech, do we start

by mapping words or morphemes tomeaning units and construct the meaningof larger units from this mapping,

or do we start with expectations andhypotheses about the meaning of a specificword or utterance based on backgroundknowledge, situation, and linguisticcontext?

or do the two types of processing interactand, if so, how?


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Models for wordprocessing

Many of the earlier studies, andpresent-day studies as well, arebased on serial models, such as

Garretts (1982) or

Levelts (1989) model of speech

production or

the PALPA model (Kay, Lesser &Coltheart, 1992) of speechrecognition/comprehension,

as well as the search and cohortmodels for visual and auditory wordrecognition presented below.


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Interactive activationmodels

Interactive activation models,simulated in artificial neural

networks (ANN) are, however,

being used more and more,

for example, the TRACE modelfor recognition/ comprehension

and

the IAM model for production

used by Dell and coworkers


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Word comprehensionmodels


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Forsters active search model Mortons logogen model, which

posit a passively responsive

lexicon where different units are

activated by incoming stimuli

the cohort model proposed by

the TRACE model of


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Active direct searchmodels

In an active, direct search lexicon, itis assumed that one searches formatches of an incoming stimulusword in bins containing wordrepresentations (auditory or visual)

which are ordered by someprinciple, for example, howfrequently they have beenencountered. The wordrepresentations in the bins are then

linked to a lexical master file,where phonological and semanticcross-references exist. Similarly, aword can be accessed from asemantic representation in

production.


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Passive indirectresponsive models

In a passive, indirect, responsivemodel, like the logogen model,auditory and visual incoming wordstimuli can activate a specificlogogen (recognition unit) if the

stimulus is strong enough (i.e.,contains enough activation and nottoo much inhibition in relation to thefeatures of the logogen to get overits activation threshold). The

logogens are also connected to asemantic cognitive lexicon, whichcan increase or decrease theactivation and thus affect whichlogogen is activated.


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Cohort model

A cohortmodel stresses theincremental build-up ofactivation as, for example, awritten word is encounteredletter by letter and a particularword is selected at a particulardecision point. An earlyperceptual analysis determinesthat a set of words are possible

candidates and recognitionproceeds by eliminating thecandidates from left to right


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The TRACE model

The TRACEmodel is a highlyinteractive model for spoken

word recognition, emphasizing

top-down processing, or

dependence on the context, inword recognition. It claims that

lexical knowledge helps

acoustic perceptual processes.


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Lexical DecisionExperiment

4040Infrequent

bisyllabic

nouns

4040Frequent

bisyllabic

nouns

Nonwords(made by

changing

letters in

realwords)

Words


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Semantic priming

A specific instance of the lexical decisiontask is semantic priming, where the

relationship between two stimuli isinvestigated.

The first stimulus is presented, followed bythe second, which is the target word todecide on (as a real word or a nonword).Semantic priming tasks can establishpatterns of association.

Semantically related word as prime wordfacilitates the recognition (lexical decision)of the target word, when compared to aunrelated prime word.

For example, the word orange isrecognized faster as a real word if it hasbeen preceded by the prime word apple,than if it has been preceded by, forexample, the word chair.


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Effects in word recognition that modelshave to explain

- The frequency effect: The more frequent aword is, the faster it is recognized.

- The length effect: The shorter a word is, thefaster it is recognized.

- The concreteness effect: The more concrete aword is, the faster it is recognized.

- The word superiority effect: A letter isrecognized faster in a word than if it occurs inisolation.

- The word/nonword effect: Words are identified

as words faster than nonwords are identified asnonwords.

- The context effect: words are identified fasterin context.

- The degradation or stimulus quality effect: A wordthat is presented clearly is recognized faster than a

word that is blurred in some way (e.g., covered by agrid), if it is presented visually.


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Word production models

Garretts (1982a) productionmodel and

Levelts (1989) model for

speaking are examples of

influential serialproductionmodels

Interactive activation models

have been presented by Delland

coworkers, Harley,and others


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Levelts model forspeech production


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Counter evidence to

serial production Blends, where two word forms are

combined in the word that is finally

produced - lexical semantics and

phonology can mutually influence eachother.

E.g. plower, combiningplantandflower.

Substitutions where thetarget and the

substitute have both a semantic and aphonological relation (e.g., catfor rat,

thumb for tongue) are much more frequent

than one would expect if the two levels did

not interrelate in some way

But the interaction is limited, so thatprocessing is only semantic at first, while

in the last stages phonology seems to

dominate.


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Simulation of aphasicword substitutions

Simulations of aphasic word substitutionshave been done, using artificial neuralnetworks

- modeling the interaction betweenphonology and semantics.

Interactive activation models are

nonmodular (i.e., each process is not self-contained).

Activation spreads bidirectionally in acontinuous flow. In this way, earlier andlater stages of processing influence each

other.A compromise model which is interactivebut contains a lexical and a phonologicalstage was developed by Dell et al. (1997)and can be used as an example.


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Dells ANN modelIt is a localistmodel, that is, nodescorrespond to psychologicalproperties (one-to-one).

Three levels of nodes are included:semantic features

known words

phonemes

All connections between nodes areexcitatory and bidirectional. Allconnections have the same (preset)weightand there is a preset decayfactor (which determines how fastthe activation of nodes decays) andnormally distributed noise. Externalupdating is used initially byactivating the semantic features ofthe target word.


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Simulation - semantic vsphonological errors

This model allows simulation ofdissociations between patients with mostlysemantic and mostly phonological errors.

Lesions affecting the decay factorproduced semantic, mixed, and formalerrors. If they were not severe, there was a

semantic component in most errors.Lesions affecting connection weight, onthe other hand, produced mostlyphonological errors.

Combinations of the two types of lesions

resulted in intermediate, mixed patterns.The model could also simulate longitudinaldata for the patients, with the same factorssimulating the later stage, only closer tonormal values.


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Therapy

Lexical-semantic research at thesingle-word level has inspired anumber of therapy methods, whichare designed to train wordassociation patterns, for example,

- Lurias restoration therapy(Luria, 1963),

- Deblocking therapy (Weigl &Bierwisch, 1970),

- BOX therapy (Visch-Brink,Bajema, & Van de Sandt-Koenderman, 1997)

- Semantic Association therapy(e.g., Martin & Laine, 2000).


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Assignments


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Look at the following list ofsemantic word substitutions:

1. football -> balloon

2. hose -> house

3. poodle -> lion

4. zebra -> trunk

5. donkey -> horse

6. doll -> cap

7. boy -> man

8. spade -> garden thing

9. orange -> apple

10. green -> purple

Try to explain each substitution:(a) in terms of semantic fields, prototype

theory, or semantic distinctive features;

(b) in terms of one or more diagnoses,indicating in which patients such a

substitution might occur;(c) in terms of what type of model a serial(Levelt-type) model or an interactive

activation (Dell-type) model you thinkwould best explain the substitution.


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Lexical Semantic