Speech and motor speech disorders and intelligibility in adolescents with Down syndrome

Figures & data

Figure 1. Intelligibility Index (II) scores and ordinal intelligibility index (OII) classification findings for 50 adolescents with Down syndrome.

Table 1. Risk factors and intelligibility findings for 45 participants with Down syndrome.

		Ordinal Intelligibility Index Classification
		Descriptive Statistics
		Low and Low + Moderate				High				Inferential Statistics
Risk Factor	Total	n	% of Participants	M	SD	n	% of Particpants	M	SD	Confidence Interval	Effect Size^a,b,c
Demographic
Males
L v H	19	9	47.4			10	52.6			−0.362, 0.257	−0.053
L + M v H	25	15	60.0			10	40.0			−0.033, 0.437	0.201
Females
L v H	17	7	41.2			10	58.8			−0.523, 0.168	−0.177
L + M v H	20	10	50.0			10	50.0			−0.294, 0.294	0.000
L Males v L Females		9	47.4							−0.258, 0.508	0.125
		7	41.2
L + M Males v L + M Females		15	60.0							−0.073, 0.476	0.201
		10	40.0
Chronological Age (years)  L v H		16		13.7	2.1	20		14.1	2.3	−0.84, 0.48	−0.18
L + M v H		25		14.2	2.3	20		14.1	2.3	−0.55, 0.63	0.04
Non-Verbal Age (years) ^d  L v H		15		4.5	1.1	18		5.0	1.5	−1.06, 0.33	−0.37
L + M v H		24		4.5	1.1	18		5.0	1.5	−1.00, 0.23	−0.38
Intelligence^d
L v H		14		43.4	7.0	18		44.4	6.2	−0.85, 0.55	−0.15
L + M v H		23		42.1	6.4	18		44.4	6.2	−0.98, 0.26	−0.36
Language
Average Words/Utterance (AWU)  L v H		16		3.8	1.3	20		4.9	2.0	−1.30, 0.05	−0.62
L + M v H		25		4.3	1.8	20		4.9	2.0	−0.90, 0.28	−0.31
OWLS^e
Listening Comprehension  L v H		6		43.5	5.0	7		48.1	6.1	−1.89, 0.37	−0.76
L + M v H		7		43.0	4.8	7		48.1	6.1	−1.97, 0.23	−0.87
Oral Expression  L v H		6		40.0	0.0	7		44.3	8.4	−1.76, 0.47	−0.64
L + M v H		7		40.0	0.0	7		44.3	8.4	−1.75, 0.40	−0.68
Oral Composite  L v H		6		40.7	1.6	7		44.7	5.5	−2.03, 0.26	−0.89
L + M v H		7		40.6	1.5	7		44.7	5.5	−2.06, 0.15	−0.95

L = Low; M = Moderate; H = High.

^a Hedges and Olkin (1985). Statistical methods for metaanalysis. Boston, MA: Academic Press.

^b Cohen (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). New Jersey: Lawrence Erlbaum Associates.

^c Effect Size: Small (S) ≥0.2; Medium (M) ≥0.5; Large (L) ≥0.8; Very Large (V) ≥1.0; Extremely Large (E) ≥2.0.

^d Kaufman and Kaufman (2004). Kaufman Brief Intelligence Test Second Edition (KBIT-2). San Antonio, TX: Pearson Assessments; Thorndike, Hagen, and Sattler (1986). Stanford-Binet Intelligence Scale, 4^th edition. Chicago: Riverside.

^e Carrow-Woolfolk (1995). Oral and Written Language Scales (OWLS): Bloomington, MN: Pearson Assessment.

Table 2. Intelligibility findings for 45 participants with Down syndrome classified by their speech and motor speech status.

Speech Disorders Classification System Summary (SDCSS): Group
		Motor Speech Classification					Totals
Speech Classification		No Motor Speech Disorder (No MSD)	Speech Motor Delay (SMD)	Childhood Dysarthria (CD)	Childhood Apraxia of Speech (CAS)	Childhood Dysarthria and Childhood Apraxia of Speech (CD & CAS)	n	%
Normal(ized) Speech Acquisition
High Intelligibility		0 (0.0)	0 (0.0)	1 (100.0)	0 (0.0)	0 (0.0)	1	2.2
Moderate Intelligibility		0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0	0.0
Low Intelligibility		0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0	0.0
Speech Errors/Persistent Speech Errors
High Intelligibility		0 (0.0)	0 (0.0)	0 (0.0)	1 (100.0)	0 (0.0)	1	2.2
Moderate Intelligibility		0 (0.0)	1 (100.0)	0 (0.0)	0 (0.0)	0 (0.0)	1	2.2
Low Intelligibility		0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0	0.0
Speech Delay/ Persistent Speech Delay
High Intelligibility		1 (100.0)	8 (72.7)	6 (37.5)	1 (25.0)	2 (20.0)	18	40.0
Moderate Intelligibility		0 (0.0)	1 (9.1)	3 (18.8)	0 (0.0)	4 (40.0)	8	17.8
Low Intelligibility		0 (0.0)	2 (18.2)	7 (43.8)	3 (75.0)	4 (40.0)	16	35.6
Totals	n	1	12	17	5	10	45
	%	2.2	26.7	37.8	11.1	22.2		100.0

Table 3. Intelligibility findings for 45 participants with Down syndrome classified by their motor speech status.

		Ordinal Intelligibility Index Classification
		Descriptive Statistics
		Low and Low + Moderate		High		Inferential Statistics
Motor Speech Disorder	Total n	n	% of Participants	n	% of Participants	Confidence Interval	Effect Size^a,b,c
Speech Motor Delay
Low v High	10	2	20.0	8	80.0	−1.232, -0.056	−0.643 M
Low + Moderate v High	12	4	33.3	8	66.7	−0.830, 0.150	−0.340
Childhood Dysarthria
Low v High	14	7	50.0	7	50.0	−0.420, 0.420	0.000
Low + Moderate v High	17	10	58.8	7	41.2	−0.168, 0.523	0.177
Childhood Apraxia of Speech
Low v High	5	3	60.0	2	40.0	−0.975, 1.377	0.201
Low + Moderate v High	5	3	60.0	2	40.0	−0.975, 1.377	0.201
Childhood Dysarthria & Childhood Apraxia of Speech
Low v High	6	4	66.7	2	33.3	−0.640, 1.320	0.340
Low + Moderate v High	10	8	80.0	2	20.0	0.056, 1.232	0.644 M
Childhood Dysarthria, Childhood Apraxia of Speech, Childhood Dysarthria & Childhood Apraxia of Speech
Low v High	25	14	56.0	11	44.0	−0.115, 0.355	0.120
Low + Moderate v High	32	21	65.6	11	34.4	0.134, 0.502	0.318 S

^a Hedges and Olkin (1985). Statistical methods for metaanalysis. Boston, MA: Academic Press.

^b Cohen (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). New Jersey: Lawrence Erlbaum Associates.

^c Effect Size: Small (S) ≥0.2; Medium (M) ≥0.5; Large (L) ≥0.8; Very Large (V) ≥1.0; Extremely Large (E) ≥2.0.

Figure 2. Subtypes of dysarthria as explanatory constructs for low intelligibility in adolescents with Down syndrome. Panel A includes the mean percentage scores on each of the dysarthria subtype indices for participants with high and low intelligibility, and panel B includes the mean percentile scores on each index for participants with high and low intelligibility.

Figure 3. Comparative information on diagnostic classifications of motor speech status as an explanatory construct for reduced intelligibility in adolescents with Down syndrome. Figure 3a includes intelligibility findings for 45 speakers with DS in the original sample. Figure 3b includes intelligibility findings for 301 speakers with seven types of complex neurodevelopmental disorders (Shriberg, Strand, et al., 2019). Figure 3c includes intelligibility findings for 415 speakers with idiopathic Speech delay (Shriberg, Campbell, et al., 2019). No MSD: No Motor Speech disorder; SMD: Speech Motor delay; CD: Childhood Dysarthria; CAS: Childhood Apraxia of Speech: CD & CAS: Concurrent CD & CAS.

Figure 4. Four measures of consonant and vowel production in Conversational Speech (CS) in adolescents with Down syndrome. In each of the four panels, filled circles indicate participants with High (H) intelligibility; open circles indicate participants with Low (L) intelligibility. Statistically significant comparisons in the upper numeric section of each panel are indicated both by boxes around them and by effect size information.

Figure 5. Sibilant distortions and intelligibility in Conversational Speech (CS) in adolescents with Down syndrome. Filled circles indicate participants with High (H) intelligibility; open circles indicate participants with Low (L) intelligibility.

Figure 6. Inappropriate prosody and voice and intelligibility in Conversational Speech (CS) in adolescents with Down syndrome. Filled circles indicate participants with High (H) intelligibility; open circles indicate participants with Low (L) intelligibility. See text for description of the data in each panel.

Hedges, L. V., & Olkin, I. (1985). Statistical methods for metaanalysis. Boston, MA: Academic Press.

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Cohen, J. (1988). Statistical power analysis for the behavioral sciences ((2nd ed.). New Jersey: Lawrence Erlbaum Associates.

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Kaufman, A. S., & Kaufman, N. L. (2004). Kaufman Brief Intelligence Test – Second Edition (KBIT-2). San Antonio, TX: Pearson Assessments.

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Thorndike, R. L., Hagen, E. P., & Sattler, J. M. (1986). Stanford-Binet intelligence scale (4th ed.). Chicago, IL: Riverside.

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Carrow-Woolfolk, E. (1995). Oral and written language scales (OWLS). Bloomington, MN: Pearson Assessment.

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Shriberg, L. D., Strand, E. A., Jakielski, K. J., & Mabie, H. L. (2019). Estimates of the prevalence of speech and motor speech disorders in persons with complex neurodevelopmental disorders. Clinical Linguistics & Phonetics. doi:10.1080/02699206.2019.1595732

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Shriberg, L. D., Campbell, T. F., Mabie, H. L., & McGlothlin, J. H. (2019). Initial studies of the phenotype and persistence of Speech Motor Delay (SMD). Clinical Linguistics & Phonetics. doi:10.1080/02699206.2019.1595733

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