Distinguishing phonetic processing and motor processing:

Evidence from instrumental analysis of acquired speech impairment

Adam BuchwaldNew York Universitybuchwald@nyu.edu

18 June 2009

DEPARTMENT OF COMMUNICATIVE SCIENCES AND DISORDERS

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Spoken language production

• Producing spoken language requires many levels and processes to be orchestrated– Lexical access in long-term memory; working

memory; articulatory planning and implementation

• Today: relationship between phonetic planning and motor programming– Guided by discussion of:

• Phonetic processing/impairment vs. motor processing/impairment in Apraxia of Speech

• Focus on: Consonant clusters

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Phonetic plans & motor programs

• “Phonetic plan” ≡ sound structure representation–includes detail re: temporal overlap of gestures, phasing relations–gestural score in articulatory phonology (Browman & Goldstein, 1986,1988, et seq.)

• As in the output of phonetic encoding in some processing accounts (Levelt et al., 1999; Cholin et al., 2004, 2006)

• “Motor programs” ≡ detailed representation encoding temporal overlap of articulators

• Inter-articulator coordination

Are these created by separate systems?

What are the properties of impairment to these systems?

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Consonant clusters

• Syllables with onset clusters contain complex structure and phasing– Onset consonants are coupled to vowels (Browman & Goldstein, 1988;

Byrd, 1996)• Center of consonant timed to onset of vowel• Complicated by presence of a cluster; in English, center of cluster timed to onset of vowel

– Multiple possible ‘repairs’ (or simplifications)• Deletion; changing phasing relation; inserting a vowel

Questions regarding 2 different aphasic/apraxic speaker • How are the consonant clusters repaired?• What properties determine the nature of the repair?

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VBRBuchwald, Rapp & Stone, 2007

• 57, RH, F

• Suffered CVA at 51– large LH fronto-parietal

infarct involving posterior frontal lobe, including Broca's area, pre- and post-central gyri and the SMG

• Dysfluent spoken production, mainly single-word utterances

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VBR and schwa insertion

• Difficulty producing complex onsets– Produces consonant clusters with a vowel inserted

between the two consonants– e.g., bleed [bəlid]

• Robust pattern– Occurs with different modalities of presentation

(naming, repetition, reading)

• What is the nature of these errors?– Epenthesis vs. Articulatory (mis)timing

believe

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Epenthesis vs. Mistiming

Epenthesis

C1 C2

• Vowel inserted in gestural score

Gestural mistiming

C1 C2

• Consonant gestures mistimed–Audible release of C1

Open vocal tract

Target:

C1 C2

əə

onset

target release

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Ultrasound study

• Examine articulations to see whether inserted schwa is like lexical schwa

• Produce word pairs: bleed-believe– Matched on C1, C2, and stressed V

• Compare tongue contours – If epenthesis: inserted schwa = lexical schwa

– If mistiming: inserted schwa ≠ lexical schwa

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Inserted schwa = Lexical schwa

Back Tongue Position Front

Red – Inserted

Blue – Lexical

Within-category differences

EQUAL

across-category differences

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Consonant cluster repair: schwa epenthesis

• The inserted vowel is the result of epenthesis– Articulatory data from ultrasound: tongue contour of

inserted vowel similar to lexical vowel• Similar variability between vowels and within vowel types• Supported by acoustic data (duration, variability, co-

articulation)

• Systematic epenthesis repair of obstruent-sonorant clusters– Removes structural (and articulatory) complexity by

adding schwa to phonetic plan

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DLEBuchwald, Rapp & Miozzo, 2009

• 72 year old aphasic/apraxic speaker• Spoken production limited – short phrases; labored • Produces systematic consonant cluster errors in

deletion of /s/ from /s/-stop and /s/-nasal clusters

• Question: at what level does deletion take place? – Is deletion part of phonetic plan or does it occur during

generation of motor program?

smash mashsteer tier deer

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Phonetic errors vs. motor errors

• Phonetic planning precedes motor programming• If phonetic plan has no /s/, then the token has singleton onset

consonant and should be produced accordingly• If phonetic plan has /s/ and deletion occurs at motor level, then

timing should be appropriate for cluster– Compare tokens with deleted /s/ to singletons– Use acoustic properties of language to help with this

• /s/-stops: VOT in spin is closer to bin than pin• /s/-nasals: nasal duration in snail shorter than nasal in nail

– Paired comparisons of target clusters with singletons• e.g., speak vs. peak, beak• e.g., smash vs. mash

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Hypotheses

• Phonetic planning errors– Stops in deletions more similar to singleton voiceless stops

• Reflects /s/ being absent from phonetic plan

– Nasals in deletions same duration as singleton nasals• Reflects /s/ being absent from phonetic plan

• Motor programming errors– Stops in deletions more similar to singleton voiced stops

• Reflects /s/ being absent from phonetic plan

– Nasals in deletions shorter than singleton nasals• Reflects /s/ being absent from phonetic plan

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/s/-stop and singleton stop VOT

• What factors increase the likelihood of repair?

Labial Alveolar Velar

(s)-stop 27.5 44.4 68.5

voiceless 30.5 43.9 77.8

voiced 21.9 33.8 44.3

N 79 103 25

Labial Alveolar

Velar

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/s/-nasal duration

020406080

100120140

sN N

dura

tion

(in m

s)

• Nasal duration and VOT both reflect the production of a phonetic plan generated without an /s/

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Phonetic planning errors

• These two cases of apraxia both exhibit phonetic planning errors– Does not mean these are the only possible errors; just

happens to be the case here

• What to do with these errors?– Examine factors that influence the incidence and

nature of these errors to learn about phonetic planning system

– For each individual, we see effects of (relatively abstract) phonological representations on their errors

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Phonological effects: VBR

• VBR: epenthesis errors in obstruent-sonorant clusters– Words with C/j/ onset (e.g., cute) argued to have complex

vocalic diphthong (/ju/) rather than cluster

• If #Cw sequences (as in queen, quote) are clusters:– Should be repaired via epenthesis

• If #Cj as in cute, music are clusters:– Should be repaired via epenthesis, as other clusters

– Never repaired via epenthesis– Repaired via deletion: /kjut/ [kut]

cute music

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Phonological effects: DLE

• DLE: /s/-deletion in obstruent-obstruent and obstruent-nasal clusters– English has a few other obstruent-obstruent and

obstruent-nasal onsets (/∫/-initial)

• If DLE’s ‘repair’ can be expressed over natural classes, should similarly affect these sequences

– In addition, other sonority-based descriptions affect error rate – deletion very rare in /sl/ and /∫r/ clusters

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Summary and future directions

• Instrumental analyses of apraxic/aphasic speech can show errors of phonetic planning– Phonetic planning errors appear to be affected by phonological

properties, leading to systematic sound structure repairs

• Future work– Explore error systematicity as a way to determine whether errors

– Extend analyses to other impairments, particularly motor programming impairment and children with speech sound impairments (with HBK, CR)

– Incorporate other speech production instruments (EMMA? Real-time MRI?)

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Acknowledgements

Brenda Rapp

Maureen Stone

Michele Miozzo

Paul Smolensky

VBR

DLECettina Chiarelli

Cristina Sanchez