Recent Modelsof Stuttering

Western Illinois UniversityFebruary 7, 1997

J. Scott Yaruss, Ph.D., CCC-SLPUniversity of Pittsburgh

Purpose

• To discuss two recent theoretical models of stuttering

• Covert Repair Hypothesis(Postma & Kolk, 1993)

• Neuropsycholinguistic Model(Perkins, Kent, & Curlee, 1991)

Some Factors That May BeInvolved in Stuttering

Genetic Environmental

Linguistic Motoric Psychological

Basic Steps inLanguage Formulation

– Figuring out what you want to say• Basic message• Pragmatic intent

– Figuring out how you want to say it• Grammatical structure• Specific words• Sounds in the words• Prosody

Levelt’s (1989) “Blueprint for the Speaker”CONCEPTUALIZER

messagegeneration

monitoring

grammaticalencoding

phonologicalencoding

preverbal message

FORMULATOR

LEXICON

lemmas

forms

phonetic plan(internal speech)

ARTICULATOR AUDITION

parsed speech

discourse model,situation knowledge,

encyclopediaetc.

phonetic string

overt speech

SPEECH-COMPREHENSION

SYSTEM

surfacestructure

Covert Repair Hypothesis (CRH)(Postma & Kolk, 1993)

• Designed to explain the production of speech disfluencies by adults who do stutter as well as those who do not in the context of general language models

• Based upon current psycholinguistic models of speech production(e.g., Dell, 1988; Levelt, 1989)

Theoretical Foundationsof the CRH—I

• Levelt’s “blueprint for the speaker”

– Describes conceptualization, formulation,

articulation, audition, and comprehension

– Explains how speakers monitor the accuracy and

appropriateness of their speech—both before and after

speech is produced

– Describes processes speakers can utilize to repair

detected errors in their phonetic plan by interrupting

ongoing speech (e.g., Levelt, 1983)

CONCEPTUALIZER

messagegeneration

monitoring

grammaticalencoding

phonologicalencoding

preverbal message

FORMULATOR

LEXICON

lemmas

forms

phonetic plan(internal speech)

ARTICULATOR AUDITION

parsed speech

discourse model,situation knowledge,

encyclopediaetc.

phonetic string

overt speech

SPEECH-COMPREHENSION

SYSTEM

surfacestructure

Levelt’s (1989) “Blueprint for the Speaker”

Levelt’s Monitoring Loops

• Internal Loops– In conceptualizer, before preverbal message is generated

– After phonetic plan is generated by formulator (covert speech)

• External Loop– After speech is articulated (overt speech)

CONCEPTUALIZERMONITOR

COMPREHENSION

AUDITIONARTICULATOR

FORMULATORSPEECH

SYSTEM

overt speech

phonetic plan(internal speech)

parsed speechpreverbal message

INTERNALLOOP

EXTERNALLOOP

phonetic string

Theoretical foundationsof the CRH—II

• Dell’s (1988) Spreading-Activation Model of Phonological Encoding

– Connectionist model

– Describes how phonological units are selected (and mis-selected)

– When a node is activated at one level, activation spreads to all connected nodes at other levels

– Node with highest degree of activation is selected

Connectionist Models

N

S

VP

V

NP

det N

SYNTACTIC LEVEL

WORD WORD

Sdet

SN

WORD

Stem

SV Af

MORPHOLOGICAL LEVEL

Co

SYL

RimeOn

Nu

PHONOLOGICAL LEVEL

TACTIC FRAMES

pastVN pl.

Stem

Af1 2

THESdet S

CAT

LEXICAL NETWORK

kOn

æNu

tCo

THE CAT JUMPDet N

Past

V

JUMPSV

–EDAf

-S

sCo

Plural

Af1 2

Spreading-Activation and Phonological Errors

æk

cat

t p

capMorphologicalLevel

PhonologicalLevel

upward

Direction ofSpreading Activation

downward

Basic Assumptionsof the CRH

• All speakers experience occasional errors in their phonetic plan due to mis-selection of phonological units

• If errors are detected, they can be repaired; repairs result in disfluencies– Disfluencies are the by-product of

speaker’s attempt to repair phonetic plans errors

Basic Assumptionsof the CRH (cont.)

• Individuals who stutter produce more disfluencies because they are assumed to…– have a slow phonological encoding mechanism

– attempt to begin speaking too soon or try to speak too quickly for their impaired encoding mechanism to make accurate selections

• The result is many phonetic plan errors and many opportunities for disfluencies

Delayed Phonological Encoding(after Yaruss & Conture, 1996)

0

ActivationLevel

timeTime of Selection

0

TUCU

CUTU

TUCUActivation

LevelNormal Activation

TU > CU

timeTime of Selection

High

Low

High

Low

Delayed Activation

TU = Target Unit CU = Competing Unit

What the CRH does anddoes not attempt to explain

• Does attempt to explain– The production of speech disfluencies in the

framework of normal language processes believed to be exhibited by all speakers

• Does not attempt to explain:– The developmental course of stuttering (e.g.,

repetitions prolongations, etc.)– The development of accessory behaviors

(struggle, tension, etc.)

CRH Summary• Speakers have the ability to monitor their speech— both

before and after it is produced

• Speakers sometimes make errors in phonological encoding due to the spreading-activation mechanism

• If speakers detect these errors, they can interrupt speech to repair them before they are produced

• The by-product of the interruption is a disfluency

• People who stutter produce more disfluencies because their phonological encoding mechanism is assumed to be impaired so there are frequent encoding errors

Neuropsycholinguistic ModelPerkins, Kent, & Curlee (1991)

• Speech involves many concurrent language and motoric processes

• The timing of the interactions between these processes is crucial– This model, like the CRH, emphasizes timing,

but now we’re interested in timing between language components

– Also called the “temporal dyssynchrony” model

Neuropsycholinguistic ModelPerkins, Kent, & Curlee, 1991

SEGMENTAL SYSTEMPhonetic Specifications

COGNITIVE SYSTEMFormulation of ideas

LANGUAGE SYSTEM Symbol System

Symbolic Mapping

WORKINGMEMORYSYSTEM

Awareness

Product of processinghigh in awareness

Stress, intonation, duration, and vocal quality

PP SYSTEM

paralinguistic

prosody

SPEECH MOTOR CONTROL SYSTEM

Segments

INTEGRATOR SYSTEMSegments integrated into syllables

Syllable S

lots

Segm

ent order

Processing procedures low in awareness

Vocal signal systemFeeling and intent mapping

Integration of paralinguisticand

prosodic components

Words for

phonemic analysis

Assumptions of the Neuropsycholinguistic Model

• Disfluencies occur due to a disruption in timing between various linguistic formulation and motoric execution

• Stuttering is defined as a “loss of control” which occurs when the individual is unable to continue speaking, but does not know why

“Loss of Control”

• Some aspects of language formulation are accessible to conscious awareness

• Others aspects (e.g., phonological encoding, integration) are not

• Loss of control occurs when disruption takes place in an aspect of the model that is not “accessible”

One Unique Aspects of the Model

• Time pressure– The pressure a speaker feels to continue

speaking when he is experiencing a disruption in linguistic/motoric integration

– Increases the likelihood that the “loss of control” feeling will occur

– Without abnormal time pressure, speech disfluencies may occur, but stuttering will not

Summary of Neuropsycholinguistic Model

• Speech requires integration of several aspects of linguistic formulation with motoric execution

• Processes can become disrupted– If disruption is “accessible” to awareness, then a

disfluency will occur. If not, the speaker will experience a loss of control

– If the loss of control is accompanied by abnormal time pressure, stuttering will occur

What do these models tell us about the diagnosis and

treatment of individual people who stutter?

?

? ?

?

Not Much!(yet)

However, the general language models on which they are based can provide guidelines about specific aspects of

language that should be examine in the diagnosis of individuals who stutter

CONCEPTUALIZER

messagegeneration

monitoring

grammaticalencoding

phonologicalencoding

preverbal message

FORMULATOR

LEXICON

lemmas

forms

phonetic plan(internal speech)

ARTICULATOR AUDITION

parsed speech

discourse model,situation knowledge,

encyclopediaetc.

phonetic string

overt speech

SPEECH-COMPREHENSION

SYSTEM

surfacestructure

Levelt’s (1989) “Blueprint for the Speaker”

Conceptualization

• Basic Message– Does client stutter more on complex messages?

– Does client stutter more on utterances with greater propositionality or meaning?

• Pragmatic Intent– How does social interaction affect fluency?

– Does client stutter more when experiencing greater demands on pragmatic or social interaction skills?

CONCEPTUALIZER

messagegeneration

monitoring

FormulationGrammatical Encoding

• Does client stutter more in situations which require more complex utterances?

• Does client stutter more on syntactically complex utterances?

• Does client demonstrate problems with syntactic development which might interfere with fluent speech production?

grammaticalencoding

phonologicalencoding

FORMULATOR

surfacestructure

FormulationLexical Access

• Does client exhibit word finding problems that might interfere with speech production?

• Does client exhibit frequent mislabelings or nonsystematic speech errors which might interfere with fluent speech production?

• Are some words harder to retrieve than others?

LEXICON

lemmas

forms

FORMULATOR

phonologicalencoding

grammaticalencoding

grammaticalencoding

phonologicalencoding

FORMULATOR

surfacestructure

FormulationPhonological Encoding

• Does client frequently produce nonsystematic speech errors which might lead to production self-repairs or speech disfluencies?

• Does client have difficulty retrieving the phonological form of utterances (as in the “tip of the tongue” phenomenon)?

Formulation Phonological Development

• Does client exhibit phonological delay which might indicate a slow-to-develop linguistic formulation system?

• Does client exhibit phonological delay which makes communication more difficult and increases sensitivity about his/her speech?

phonologicalencoding

phonetic plan(internal speech)

ARTICULATOR

FORMULATOR

Articulation

• Does client stutter more when using a faster speaking rate?

• Does client stutter more when leaving less time for linguistic planning and formulation of utterances?

• Does client have difficulties with diadochokinetic (DDK) abilities that might interfere with ability to rapidly and precisely produce speech

Summary

• Several recent models of stuttering have emphasized the role of language formulation

• These models are important for improving our understanding of the nature of stuttering, in part because of the research they encourage

• An increased understanding of the language models on which these theories are based can help us improve the diagnosis of stuttering