This document describes a model of speech processing and underlying deficits in speech sound disorders. It outlines the stages of speech processing including perception, phonological rules, phonetic planning and motor execution. It discusses evidence for the model from phenomena like the McGurk effect. The document then examines different types of speech sound disorders including articulation disorders, phonological delay, consistent phonological disorder, and inconsistent phonological disorder. It analyzes the underlying deficits for each type based on performance across different tasks and relates these to specific impairments in the speech processing model.

1. A Model of speech processing
and underlying deficits in speech
sound disorders
Aileen Wright
SL6003 3.1 2012

2. Obligatory Reading
• Differential Diagnosis of phonological
disorders in Dodd (2005)

3. Learning objectives
Describe the stages and routes used in processing speech
in Duggierala & Dodd’s model
Describe what happens if different parts of the model
break down
Explain the underlying deficits in each category in Dodd’s
classification of speech sound disorders
Explain the consequences of the underlying deficits for the
child’s speech
Be able to differentially diagnose the type of speech sound
disorder from an analysis of speech

4. The McGurk effect
• http://www.youtube.com/watch?NR=1&v=I1X
WDOwH47Y

5. Evidence: how do you account for this?
• Children are taken in by the McGurk effect (Dodd & McCormack
2008)
• Children can usually recognise spoken word pairs that they are
unable to differentiate in production
• Children can imitate nonsense words
• Children can sometimes pronounce real words better in imitation
than in spontaneous speech
• Children’s speech errors are characterised by consistent errors that
can be elegantly explained by phonological processes/realisation
rules, e.g. postconsonantal sonorants delete, e.g. traintein, blue
bu, new  nu, twintin
• Children sometimes suppress processes in new words, but
processes remain in a few very early acquired words
• Children sometimes produce a word correctly, then later start using
a less accurate production

6. Comparison of Stackhouse & Wells and
Duggirala & Dodd models

7. Where the meaning of the
word is stored: Mouse 
Duggierala & Dodd’s model
small rodent, long tail, eats Analyse incoming data
cheese, lives in hole.. from both modalities to
form phonological system
Knowledge about rules of
Stored entries of words phonological system, eg legal vs
recording how they sound: illegal consonant combinations
Mouse  /maʊs/. Contain
enough information for a heard
word to be recognized as
distinct from other similar-
sounding words (e.g. TAP vs Realisation rules:
CAP; CAP vs CAT). A set of mental processes that
govern the construction of a
Pragmatic knowledge, rules of phonological plan
social interaction
Stored plans for
high frequency
Mental processes that derive artic. utterances
Instructions from abstract plan.
Includes phonetic specification of Abstract plan. Drives
phonemes. Assembles the gestural phonetic program that
targets (articulatory instructions) into sets up motor specs
correct sequence in real time, taking
into account the context, e.g.
peripheral production of speech at the level
assimilations and the appropriate
of the vocal tract. Gestures required for
intonation for a question form.
accurate pronunciation are produced in
form of overt muscular action

8. Justification of model (Dodd & McCormack 1995)
McGurk effect
Evidence:
errors are consistent
Across the board change
happens when a process
Socio-linguistic variation in is suppressed
speech eg “gay speech” Phonological therapy
generalises to untreated
targets
Munson, B. & Babel, M. 2007. Loose
Lips and Silver Tongues, or, Projecting
Sexual Orientation Through Speech
Language and Linguistics Compass 1/5
:416–449,

9. Processing routes
Input from both
McGurk effect
modalities
Input of linguistic
knowledge
Repetition of non- (constraints) to
words/unknown words realisation rules
Ready made
phonological plans
for known words

10. Levels of breakdown on the model (Dodd & McCormack 1995)
Visually impaired children
make more errors of place of CPD children showed no
artic, rather then manner, preference for legal over
unlike non VI illegal words: Performed
worse on PA tasks than
other gps. lack of knowledge
of rules of phon. system?
IC children performed worse
in receptive and expressive
vocab than Control, PD and
CPD: impaired ability to
access full forms of words?
IC children made more IC gp worse than other 3 on
phonological than phonetic errors: non-verbal motor (tracing)
phonological planning deficit rather and verbal motor (learning
than phonetic programming non words) tasks
Delayed gp showed
no specific deficit.
Just slightly behind
controls on all tasks

11. Why Speech disorders? Perceptual deficits
• Deficits in auditory processing
• Tallal & Piercy 1973, 1974,1975
YES
• Children with SLI/dyslexia have difficulties with
fast temporal processing of tones
• Coady, Kuender, Evans 2005
• No difficulty if normal speech used rather than
NO synthetic sound
• children distinguish minimal pairs they do not
produce
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12. Why speech disorders?: Cognitive-linguistic impairment:
• Children with inconsistent disorder are poorer in
expressive vocab. tests:
• Difficulty word-finding, accessing phonological
Lexical deficits?
shape of word?
• Impaired ability to access full specifications of
words  inconsistent word production
• Difficulty abstracting knowledge from mental
lexicon about nature of phonological system
• E.g. knowledge of phonological legality: Children
with consistent disorder show no preference for
Impaired rule legal over illegal nonsense names
derivation
ability? • Suggests deficit in deducing constraints inherent
in native phonological system
• E.g. phonological awareness: Children with
consistent disorder show difficulty with
recognising rhyme and alliteration
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13. Why speech disorders? Output processing
• Motor accuracy test: tracing
• Inconsistent group performed worse
Impaired than other gps
ability to • Nonsense word learning
generate • Inconsistent group performed worse
phonological than other gps
plans • Suggests inconsistent group have
motor planning problem not specific to
speech
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13

14. Why speech disorders? Motor execution
• mental processes that derive precise
Impaired articulatory instructions for the
ability to pronunciation of a word from an
generate abstract phonological plan
phonetic • Inconsistent gp: more phonological
plans? than phonetic errors, therefore no
evidence for this
Motor • Anatomical anomaly, muscle
execution disfunction
impairment • Degree?
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15. Consistent phonological disorder
Underlying deficit: rule
abstraction/pattern recognition
Determining the
statistical patterns in the
Learning which contrasts
ambient language so they
are relevant in the
can efficiently segment
ambient language
continuous speech into
word-sized units

16. Inconsistent speech disorder
Holm, Crosbie & Dodd (2007) Differentiating Normal Variability from Inconsistency in Children's Speech: Normative Data
International Journal of Language & Communication Disorders, v42 n4 p467-486
Underlying deficit: phonological planning
i.e. generating a plan that Incomplete phonological plan
specifies the sequences of leads to inadequate phonetic
programmes with articulatory
consonants and vowels to
parameters that are too broad.
be produced.
• neural messages that sequence
• Underspecified or degraded speech movements provide
phonological plans. May be due imprecise instructions.
to:
• having inaccurate phonological
representations,
• problems accessing accurate
phonological representations
• difficulty setting up the
phonological plan.
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17. Conclusions: underlying deficit
Articulation Delayed: Consistent Inconsistent
Disorder disordered: disordered:
Motor cognitive- Difficulties with
no specific
execution linguistic phonological
impairment deficit planning
deficit:
impaired Degraded
ability to phonological
derive and representations,
or difficulty
organise accessing them
knowledge
about nature
of ambient
phonological Motor planning
difficulty
system
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18. Conclusions
Skills are inter-related: impairment of one will effect others
Differing impairment profiles indicates areas of general
impairment that guide further Ax and intervention
Surface speech error patterns can be described in different ways,
but description has limited explanatory power
For profound understanding of speech disorders:
• Different profiles require different patterns of impairment
• More generic mental abilities may underlie some kinds of speech disorder
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19. Diagnosis & the Speech Processing Model
Articulation:
• difficulties in phonetic programming or motor execution
Phonological Delay:
• no apparent specific deficits in speech processing chain. Little behind control on
all tasks.
Consistent Disordered:
• often have phonological awareness difficulties, indicates a linguistic impairment in
deriving knowledge about their language system
Inconsistent:
• difficulties with phonological planning
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20. Differential Diagnosis:
Articulation disorder
Three types
• Organic ( dysarthria)
• Structural anomaly( cleft palate)
• Functional articulation disorder
Inability to produce a sound in isolation, or in any
phonetic context. Same production in spontaneous
production as on imitation
• Child cannot produce the sound.
• Differential diagnosis requires a stimulability probe
OR sound is distorted (not another phoneme) e.g.
lateralised /s/, nasal fricative for /s/
• In this case, child may be stimulable for correct sound, but has
habituated the wrong sound
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21. Differential Diagnosis:
Phonological delay
The child’s phonological error patterns
are those which occur during normal
development, but at least some are
typical of younger children
• Chronologically mismatched pattern of errors
• 6mths+ delay is significant
• Changing system or frozen system- monitor for 3mths
or home programme
• Child may catch up by themselves
• 5 years+: frozen system: not likely to change without
intervention, so needs therapy
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22. Differential Diagnosis:
Consistent Phonological Disorder
Use of non-developmental error
patterns (atypical, disordered, unusual,
idiosyncratic)
• Variety of syllable structures and stress patterns is
restricted
• May have developmental patterns also
• Only one non- developmental error means disorder
• Often have phonological awareness difficulties
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23. Differential Diagnosis:
Inconsistent Phonological Disorder
At least 40% variability e.g. when asked
to name 25 pictures on 3 occasions
• Produce same word in multiple error forms
• Not correct/incorrect: maturing system
• Lack of stability in phonological system
• Indicates a pervasive speech disorder
• Difficulties in phonological planning
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24. Differential diagnosis: (Dodd et al 2002)
Inconsistent phonological disorder
vs.developmental verbal dyspraxia (DVD)
• Inconsistent phonological disorder is frequently mis-diagnoses as DVD
• Differences:
Developmental Verbal Dyspraxia Inconsistent Phonological Disorder
Difficulties producing many sounds in Are able to produce most sounds in
isolation isolation
Frequent difficulties with oro-motor Have age appropriate oro-motor skills
skills
Imitation worse than spontaneous imitation better than spontaneous
production productions
More variable productions in different High degree of inconsistent productions
contexts of the same lexical item in the same
context- 40%
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25. Characterisation of a SSD
• Josh (4:11) presents with an inconsistent phonological disorder and some
developmental processes. Inconsistency is 56% and PCC on the DEAP is 44%.
Where he uses them, he is fronting velars and / and he is gliding /r/  /w/.
/,
Other than this his phoneme inventory is age appropriate. He uses 1, 2 and
some three syllable words. He produces /l/ blends but no other clusters.
Intelligibility is severely reduced for all listeners.
• Mary (3:6) presents with a phonological delay characterised by final
consonant deletion of all consonants except nasals and stopping of all
fricatives and affricates. She is also using the age-appropriate processes of
weak syllable deletion, cluster reduction and gliding of /r//w/. PCC on the
DEAP is 62%. Intelligibility is severely reduced for all listeners.
• Paddy (3:11) presents with a consistent phonological disorder characterised by
a very limited inventory of consonants (p, b, m ….) and structures (CV, VC,
VCV), Word initially all fricatives are produced as /h/. PCC on the DEAP is 57%.
Intelligibility is severely reduced for all listeners.
• Aoife (4:11) presents with a mild phonological delay characterised by cluster
reduction of all /s/ clusters. She also has an articulation difficulty with //.
Otherwise her inventory of phonemes and structures is age appropriate. PCC
on the DEAP is 86%. The delay is resulting in reduced intelligibility for
unfamiliar listeners.