Poster Presentation for the ASHA National Convention in New Orleans, LA (November, 2001)

The Effects of Articulatory Accuracy on Prosody in Children with Developmental Apraxia of Speech

 

Amy Skinder-Meredith, Ph.D., Carol Stoel-Gammon, Ph.D., Richard Wright, Ph.D., and Edythe Strand, Ph.D.

 

Abstract

The following study examines the interaction between segmental accuracy and prosody in 10 children, ages 4-9 years, with Developmental Apraxia of Speech.  Stimuli include nonsense words that vary in phonetic complexity.  Duration, Fo, and amplitude measures are implemented to examine if achieving articulatory accuracy negatively impacts prosody.

 

BACKGROUND

 

v    Many researchers have listed prosodic disturbances as a characteristic of Developmental Apraxia of Speech (DAS) (Crary, 1993; Robin, Hall, & Jordan 1987; Rosenbek & Wertz, 1972; Velleman & K. Strand, 1994). 

v    Researchers have debated that prosodic errors in apraxic speech may be due to an attempt to compensate for severe speech production problems (Duffy, 1995; Marquardt & Sussman, 1991; Velleman & K. Strand, 1994).

v    Rationale for a segmental-suprasegmental relationship

o      A relationship between prosody and articulation has been noted clinically for years (Rosenbek & Wertz, 1972; Velleman & Shriberg, 1999; Yoss & Darley, 1974). 

o      Neuromotor control studies (Nelson, 1983), which have examined the ‘trade-off’ between speed and accuracy of movement, also support this potential relationship.

o      Children with DAS experience difficulty with accurate speech production at normal rate (Rosenthal, 1994). 

o      Children with DAS have been observed to incorporate a target phoneme at slower than normal speech rate but not able to produce it at normal speech rate (Yoss & Darley, 1974). 

v    The present study further investigates the perceptual results from a previous study, which examined the effects of phonetic complexity and stress patterns on segmental and lexical stress errors (Skinder, 2000). 

v    Results of the prior study indicated a relationship between accuracy of segments and rate of speech, where decreased rate correlated with increased accuracy.

 

 
PURPOSE

 

v    The goal of the present study is to further examine this potential segmental-suprasegmental relationship by comparing acoustic measures related to prosody [duration, fundamental frequency (Fo) and amplitude (dB SPL)] of words produced correctly (i.e., words produced with all the correct segments) to words produced incorrectly (i.e., incorrect segments, including omitted segments). 

v    A subset of data from Skinder’s (2000) previous study was used for this analysis

 

 

 

HYPOTHESES

v      It is predicted that words produced correctly will have required increased articulatory effort, which will thus have a negative impact on prosody.

 

v      Peak Fo and mean Fo differences between stressed and unstressed syllables will be less for words produced correctly than words produced incorrectly.

v      Amplitude differences between stressed and unstressed syllables will be less for words produced correctly than words produced incorrectly.

v      Total word durations will be longer in words produced correctly than words produced incorrectly

 

METHODS

 

Subjects:

v             Participants include 10 children referred with DAS ages 4;10 to 9;11 years of age. 

v             Local SLPs were sent a letter asking for children who present with the following characteristics (Davis, Jakielski & Marquardt, 1998):

  1. limited consonant and vowel repertoire,
  2. frequent omission errors,
  3. high incidence of vowel errors,
  4. inconsistent articulation errors,
  5. altered suprasegmental characteristics,
  6. increased errors on longer units of speech output,
  7. significant difficulty imitating words and phrases,
  8. predominant use of simple syllable shapes,
  9. impaired volitional oral movements,
  10. expressive skills less than receptive skills, and
  11. reduced diadochokinetic rates.

v             Inclusionary criteria:  Participants exhibited at least eight of the eleven characteristics previously listed.  At least one of these characteristics included one of the three speech characteristics suggested by Davis and colleagues (1998) as being differential characteristics for DAS:

  1. altered suprasegmental characteristics
  2. inconsistent articulation errors
  3. vowel errors 

v             Additional criteria included (a) normal hearing (b) Standard American dialect; (c) normal receptive language skills and (d) a normal structural functional examination.

v             Exclusionary criteria (a) previous acquired neuropathology, disease, or injury; (b) use of neuroleptic drugs; and (c ) cognitive delays.

 

         Children were split into two levels of impairment groups: severe and mild-moderate. Placement was based on speech intelligibility, standardized articulation measures, and percent consonants correct (PCC) scores

 

Stimuli : The following words were elicited in the carrier phrase, “I can say ______________” six times. Stimuli included nonsense words with three levels of phonetic complexity (easy, moderate, difficult) and 2 levels of lexical stress pattern [trochaic (S-W) and iambic (W-S)]. 


 

 


Acoustic Analysis

Tokens were digitized and analyzed with Multi-Speech on a CSL 4400

For each stressed and unstressed syllable the following was measured:                                  

Peak fundamental frequency (Hz): Highest point on the fo contour in the voiced segment of the syllable.

Mean fundamental frequency (Hz): Mean fo contour of the voiced segment of the syllable.

Peak amplitude (dB):  Highest point in the voiced segment of the syllable on the amplitude trace.

Mean amplitude (dB): Mean dB of the voiced segment of the syllable.

Total word duration (ms): Offset of the word – onset of the word

 

 

Data Reduction:

Tokens had been perceptually judged in the prior study as segmentally correct and incorrect by graduate student clinicians

For total word durations, 104 tokens were used to compare durations of correct to incorrect tokens.  Comparisons were made for each child.  I.e. Subject #1’s incorrect production of ‘stroiful’ to his correct production of ‘stroiful’.

For fundamental frequency and amplitude comparisons, correct and incorrect productions of each token were compared, regardless of the subject. However, most easy word comparisons were from children in the severe group and most moderate and difficult word comparisons were from children in the mild-moderate group.

 

 

 

 

 

 

 

 

 

RESULTS

Hypotheses were supported only on some measures depending on the phonetic complexity and stress pattern.

Figure 1a. Average differences of peak and mean fundamental frequency between stressed and unstressed syllables for words with easy phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns.

 

Figure 1b.  Average differences of peak and mean dB between stressed and unstressed syllables for words with easy phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns.

 

v    Easy trochees: Both pitch (Hz) and amplitude (dB) measures showed greater differences for incorrect than correct productions.

v    Easy iambs: Peak Hz difference was the only measure that showed a higher difference for incorrect production.

Figure 2a. Average differences of peak and mean fundamental frequency between stressed and unstressed syllables for words with moderate phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns.

Figure 2b. Average differences of peak and mean dB between stressed and unstressed syllables for words with moderate phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns

 

v    Moderate trochees: Peak Hz and peak dB differences were higher

v    Moderate iambs: only peak dB difference was higher

 

Figure 3a. Average differences of peak and mean fundamental frequency between stressed and unstressed syllables for words with difficult phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns.

Figure 3b. Average differences of peak and mean dB between stressed and unstressed syllables for words with difficult phonetic complexity.  Words produced correctly are compared to words produced incorrectly for both trochaic and iambic stress patterns.

 

v    Difficult trochees: only maximum Hz difference was higher

v    Difficult iambs: Peak and mean Hz differences were both higher for incorrect productions

v    In general, standard deviations were very high for all of these averages (see appendix)

 

 

Total word duration results were influenced by stress pattern and level of impairment.

 

Average Total Word Duration Differences between Correct and Incorrect Productions ms

Severe

trochees

iambs

avg

-3ms

-148.4ms

stdev

50ms

141.4 ms

Mild-Moderate

 

avg

130.2ms

-9ms

stdev

177.7ms

363.2ms

 

Number and type of incidences where one category of words was produced with longer word durations than the other

Severe                

 Iambs       3/4 correct productions longer than incorrect productions

Trochees   5/5 incorrect productions longer than correct productions

Mild to Moderate

Iambs        6/6 correct productions longer than incorrect productions

Trochees   6/9 incorrect productions longer than correct productions

 

v    Trochees: Correct productions were longer in more instances than incorrect production.

v    Iambs: Incorrect productions were longer in more instances than correct productions.

v    These patterns appear stronger in the children in the severe group than the mild-moderate group.

 

DISCUSSION

v    Although the compared average values are interesting, it is important to note that the standard deviations were very high.

v    High standard deviations indicate high inter-subject variability.

v    Further analysis of the individual children may lead to more interesting findings.

v    The segmental-suprasegmental relationship is revealed in different ways that the current studies methods were not always sensitive to.

v    Different case scenarios

v    Children who struggled while saying the word incorrectly, thus increasing total word duration and decreasing Hz and dB differences

v    Children who say words correctly with minimal effort, keeping suprasegmental aspects in tact.

v    Children who struggle to say the word correctly and do so at the expense of suprasegmental aspects

v    Children who say the word incorrectly and don’t struggle and keep suprasegmental aspects in tact.

v    The present study worked off of a hypothesis based on the latter two scenarios, but not the first two.

v    To better investigate the relationship between articulation and prosody, one needs to take into account ways to better measure articulatory effort.

 

REFERENCES:

Crary, M. (1993).  Developmental Motor Speech Disorders, Singular Publishing

Group, Inc., San Diego, CA.

 

Davis, B., Jakielski, K., & Marquardt, T. (1998). Developmental apraxia of speech: determiners of differential diagnosis.  Clinical Linguistics & Phonetics, 12, 25-45.

 

Duffy, J. R., (1995). Motor Speech Disorders: Substrates, Differential Diagnosis, and Management, Mosby, St. Louis, MO. pp. 259-281.

 

Marquardt, T. & Sussman, H. (1991). Developmental apraxia of speech: theory and

practice.  In D. Vogel and M. Cannito (Eds. )  Treating Disordered Speech Motor Control.

Texas, Pro-ed. 341-390.

 

Nelson, W. L. (1983). Physical principles for economies of skilled movement. Biological Cybernetics, 46(2), 135-137.

 

Robin, D. A., Hall, P.K., & Jordan, L. S. (1987). Prosodic impairment in developmental verbal apraxia. Presentation to the American Speech-Language-Hearing Association, New Orleans.

 

Rosenbek, J., & Wetz, R. T. (1972). A review of 50 cases of developmental apraxia of

speech. Language, Speech and Hearing Services in Schools, 3, 23-33.

 

Rosenthal, J. B. (1994). Rate control therapy for developmental apraxia of speech. Clinics

in Communication Disorders, 3, 190-200.

 

 

Skinder, A. (2000). The relationship of prosodic and articulatory errors produced by children with developmental apraxia of speech. Unpublished dissertation, University of Washington, Seattle.

 

Rosenbek, J. & Wertz, R. (1972). A review of 50 cases of developmental apraxic speech. Journal of Speech and Hearing Research, 26, 231-249.

 

Velleman, S. & Shriberg, L. (1999).  Metrical Analysis of the Speech of Children with suspected developmental apraxia of speech. Journal of Speech, Language, and Hearing Research, 42, 1444-1460.

 

Velleman, S.  & Strand, K. (1994). Developmental verbal dyspraxia. In J. Bernthal (Ed.),

Phonological  Characteristics of Special Populations. New York: Thieme Medical Publishers.

 

Yoss, K. A. & Darley, F. L. (1974). Developmental apraxia of speech in children with defective articulation. Journal of Speech and Hearing Research, 17, 399-416.

 


Appendix

 

 

correct easy trochees

 

incorrect easy trochees

 

AVER

SD

 

 

avg

stdev

max hz

16.1175

37.25838

 

max hz

27.4649

61.21707

Hzexc

-0.1336

9.583335

 

Hzexc

-3.0541

62.35906

mean hz

16.1088

34.42051

 

mean hz

39.3265

57.03438

meanfo

16.3319

34.69792

 

meanfo

41.6664

60.25113

 

 

 

 

 

 

 

max dB

1.9449

4.100872

 

max dB

4.8791

9.46579

dBexcur

-3.8687

6.408364

 

dBexcur

1.1296

8.395381

mean dB

2.6874

4.04583

 

mean dB

4.2296

6.501341

 

 

 

 

 

 

 

correct easy iambs

 

 

incorrect easy iambs

 

avg.

stdev

 

 

avg

stdev

max hz

5.410583

14.55373

 

max hz

10.1905

21.27774

Hzexc

5.784833

18.67807

 

Hzexc

25.51708

24.81689

mean hz

4.738417

15.87201

 

mean hz

0.829083

14.6304

meanfo

4.554167

15.47975

 

meanfo

-0.10867

14.59625

 

 

 

 

 

 

 

max dB

0.617083

4.424099

 

max dB

0.616333

5.170878

dBexcur

2.294917

4.696744

 

dBexcur

3.187667

5.35308

mean dB

1.041917

3.717542

 

mean dB

-0.42942

4.747411

 

 

 

 

 

 

 

correct moderate trochees

 

incorrect moderate trochees

 

avg.

stdev

 

 

avg

stdev

max hz

46.4761

53.83985

 

max hz

54.75742

77.61593

Hzexc

15.7014

29.85462

 

Hzexc

23.94142

16.28918

mean hz

39.6376

49.86828

 

mean hz

25.35975

48.08008

meanfo

39.9582

50.18175

 

meanfo

25.0785

48.6575

 

 

 

 

 

 

 

max dB

4.0058

2.9656

 

max dB

9.749167

19.33399

dBexcur

3.6562

9.309486

 

dBexcur

1.583

7.093766

mean dB

10.929

20.85805

 

mean dB

5.2635

3.236549

 

 

 

 

 

 

 

correct moderate iambs

 

incorrect moderate iambs

 

avg

stdev

 

 

avg.

stdev

max hz

26.18073

40.46635

 

max hz

14.22067

32.86981

Hzexc

23.21318

20.28083

 

Hzexc

9.205833

15.67648

mean hz

38.93573

72.32214

 

mean hz

5.71325

35.1999

meanfo

40.00345

76.90316

 

meanfo

5.698583

35.34041

 

 

 

 

 

 

 

max dB

4.722545

4.195045

 

max dB

6.185167

21.15819

dBexcur

3.017727

12.99188

 

dBexcur

3.576417

6.844719

mean dB

4.722545

26.59304

 

mean dB

-1.516

2.837961

 

 

 

 

 

 

 

 

correct difficult trochees

 

incorrect difficult trochees

 

avg

stdev

 

 

avg

stdev

max hz

76.1374

71.22074

 

max hz

93.27409

77.2951

Hzexc

-0.1599

23.41936

 

Hzexc

-11.8812

17.64695

mean hz

69.8973

65.03138

 

mean hz

69.57027

59.7241

meanfo

71.2037

65.82518

 

meanfo

70.906

60.65311

 

 

 

 

 

 

 

max dB

5.5586

2.836316

 

max dB

4.654818

4.91614

dBexcur

2.5052

5.854321

 

dBexcur

2.354818

3.404689

mean dB

4.6356

4.268778

 

mean dB

4.521

4.405127

 

 

 

 

 

 

 

correct difficult iambs

 

incorrect difficult iambs

 

avg.

stdv

 

 

avg

stdev

max hz

-22.7177

68.1075

 

max hz

31.08507

48.42557

Hzexc

16.6446

42.36394

 

Hzexc

32.70047

45.85923

mean hz

-24.1876

47.93952

 

mean hz

23.42373

41.31184

meanfo

-25.8302

48.31514

 

meanfo

21.9182

40.20569

 

 

 

 

 

 

 

max dB

-1.0123

6.351219

 

max dB

4.2866

5.522375

dBexcur

0.8327

5.577814

 

dBexcur

1.557733

7.637645

mean dB

0.4261

4.462514

 

mean dB

3.544933

4.990934