development

Journal of Phonetics (1986) 14, 247- 256

Phonetic characteristics of delayed /sf development ~-

Irene Stephens

Northern Illinois University, DeKalb, Illinois, U.S.A.

and Paul R. Hoffman and Raymond G. Daniloff Louisiana State University, Baton Rouge, Louisiana 70802, U.S.A. Received 8th August 1985, and in revised form 22nd March 1986

Development of phonetically acceptable jsj articulation by misarticulating 5-year-old children was assessed longitudinally . The specific error allophone produced by an individual child strongly predicted development. Children who represented jsj with a lateral fricative at the age of 5 years universally failed to develop adequate [s] articulation by the age of 8 years. Approximately 50% of the children representing j sj with a dentalized fricative acquired correct [s] production by age 8. Nearly all of the children who represented /sfwith a bladed fricative developed adequate [s] articulation. Phonetic context appeared not to differentially bias development of normal [s] articulation.

1. Introduction Cross-sectional studies of normal phonological development have indicated that phonetic production skill for the fricatives is acquired gradually and relatively late (Templin, 1957; Prather, Hedrick & Kern, 1975; Ingram, Christman, Veach & Webster, 1980). Fricatives are also among the phones most often misarticulated by children judged to have delayed speech sound development (Snow, 1963; Ingram, 1976; Hodson & Paden, 1981 ). The fricatives may provide a particularly difficult challenge to the language-learning child because they appear to require greater motor control than the stops, nasals and glides which are acquired earlier (Kent & Moll, 1972; Subtelny, Oya & Subtelny, 1972; Hardcastle, 1976; Wood, 1979). This phonetic difficulty appears in the phonological processes used to describe children's misarticulations. Such processes may reflect the inherent perceptual or motoric difficulty associated with certain sound classes (Oller & MacNeilage, 1983). The purpose of the present study was to investigate two phonetic-level influences upon delayed development of [s] production: the phonetic nature of the child's error phone and the error phone's immediate phonetic context. Ingram et a/. (1980) described a gradual phonetic approximation of [s] in normal development. In the first stage, [s] is avoided. In the next stage, [s] is produced as a stop consonant. Later, [s] is produced as either a bladed or dentalized fricative. Finally, [s] is 0095-4470/86/020247

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M. I. Stephens et al.

248 8

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Figure 1. Amplitude vs. frequency spectra of children's productions of normal (N) , dentalized (D), lateralized (L) a nd retracted (R) [s).

produced as an alveolar fricative. Similar fricative substitutions have been described for children whose phonetic acquisition is developmentally delayed . Daniloff, Wilcox & Stephens (I 980) described three [s] misarticulations. Figure I shows amplitude by frequency spectra for normal [s] and each of these error allophones. Dentalized [~] is produced with a visible tongue articulation against or between the incisors. This articulation results in a weak (low amplitude) flat and broad power spectrum which covers most of the 0- 8000 Hz range. Lateralized [s'] is produced with a central lingual constriction against the hard palate or alveolar ridge . Compared to dentalized [~], lateralized [s'] spectra are typically more intense with larger intensity peaks. Bladed or retracted [sr] is produced with a palatal constriction and a wider than usual mandibular opening. The noise produced is perceptably "hissy". The spectra typically show lower than normal energy components in addition to strong energy peaks in the frequencies above 4000Hz. These show strong coarticulatory variability across differing contexts, as well. Studies of both normal and delayed [s] development have shown effects of phonetic context. Gallagher & Shriner (I 975) found that normally developing 3-year-olds were more likely to correctly produce [s] if it was preceded and followed by consonants rather than vowels, for example in the [t1+st] context of the sentence The cat stood up. Older miscarticulating children (7 years old) have been shown to correctly articulate [s] more often in single-word consonant cluster contexts than when [s] functioned as a consonant singleton (Spriestersbach & Curtis, 1951). Within /C sCj contexts, it has been demonstrated that older, misarticulating children correctly produce [s] more often when preceded and followed by labial and velar consonants as opposed to alveolar consonants (Mazza, Schuckers & Daniloff, 1979; Haynes, Haynes & Jackson, I 982).

Delayed /s/ development

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A problem inherent to all of the studies cited above is that each child's performance was assessed at one point in time. The developmental patterns described involve extrapolations across subjects as well as across time. Diedrich & Bangert ( 1980) studied changes in [s] articulation resulting from speech therapy. Their results suggest that phonetic context did not systematically influence development of [s]. Furthermore, they found that type of error phone used, dentalized [~] or lateralized [s'] did not show a systematic relation with the course of therapy. The purpose of the present study was to longitudinally investigate the development of [s] production by 5-year-olds using the three error allophones described by Daniloff et a!. (1980). These children were considered delayed in their phonetic development inasmuch as 50% of a population of 3-year-olds would be expected to have mastered [s] articulation (Prather eta!. 1975). We wished to determine if the use of a particular error allophone would reflect differential development of [s]. We further wished to determine if place of articulation of contextual consonants affects development of [s] production . 2. Method

2.1. Subjects Fifty-three, 5-year-old children (34 males, 19 females) who misarticulated [s], and at most two other phonemes, during administration of standard picture articulation tests were utilized as subjects. All children passed a bilateral hearing screening, had no general health problems, and were judged not to have any other significant speech and language deficits. All children were drawn from a single urban school district in the midwestern U .S.A. All performed successfully in school work. The first author (a professional speech- language pathologist with 25 years of experience and an advanced degree in Linguistics, specializing in Child Language Development) categorized each child at the start of the study by careful live screening. Children producing [s] distortions containing the characteristics of an open mandible, visible tongue tip against or between the teeth, and [B)-like perceptual quality, were categorized as dentalizers. A slightly open mandible, distinctive low-pitched hushing noise, and minimal contextual variability of perceptual quality served to categorize lateralizers. For retracters, a generally non-visible lingual articulation, with moderate jaw opening, no visible dentalization or audible lateralization, and a strongly context dependent perceptual quality served as criteria for categorization. Children were distributed among allophonic types as follows : dentalizers (35), retracters (12), lateralizers (6). 2.2. Sampling procedure Children were tested individually eight times during the school year. Test sessions were scheduled during the week before and the week after the 50th, 1OOth, !50th and 200th days of the school year. Each session consisted of two sequential presentations of 34 sentences. Sentences were read by the examiner and immediately repeated by the child . Exact repetitions of sentences were required only if paraphrases did not include the targeted contexts. A period of 3- 5 min of conversation occurred between the two test sentences repetitions. Test sentences were constructed to provide a wide variety of [s] phonetic contexts, in sentences of relatively simple, but varied grammatical construction. Each sentence

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TABLE I. Stimulus sentences with target contexts underlined SA

su Is sk ts Is sp sc si ps st ps sc sn st Sl

sl sc Is sn ns su ps sn ns sl ns rs S;J

sp si ts

sn sk su sc sr SA

rs ks sr st su sr sp ps sp Sl

rs ts st sc sk ks sr ns ks sk rs ks

The sun melted the snowman . Sue bought a mask at the store. Mr. Wi~on had tomato soup for lunch. I know how to ask a quegion. She sits with a friend on the bus- -ride. A! ~ang in the Sunday school class . A spid~ ~at down beside her. Let's choose the teams. The seal picks a ball up on its nose. Mom ho~ our baby won't fu~ !:ight now. He was the lag one to fall asleep. He tri~ and falls when he runs too fag. Ann really like~ cheese. They'll have a snack as soon as they can. Don't bring a gick into the classroom. You don't plant seeds with a ~oon. If he falls on the ~ide , he rips up his pants. I like it when mom cooks chicken. Children fee! ~ad when they get a spanking. Sneak over and take a turn on the -seesaw. Ca.!!_ §_ally be a nurse at the hospital? Susie hi~ a home run every time. If candy drops on the floor, it gets dugy. Snoopy gets into mischief. Ca.!!_ ~orne kids do a skip and a jump. He's a ~ugger for the Dukes. Once mom gave me a ki~ !:ight here. That person is really handsome. On my way home I pa~ ~ mailbo~. Ted took a spill off a ~ooter. See that oldtime horse and buggy? On Halloween you'll see Io~ of spooks.

contained one or two [s] targets in 16 phonetic contexts. These included (I) word-initial prevocalic [s]; (2) [s] preceding the consonants [p, t, k, n, r, I, c]; and (3) [s] following the consonants [p, t, k, n, r, I, c]. Table I lists the sentences and tested [s] contexts. Four second-year MA-trainees in speech- language pathology served as judges, each testing from 10 to 15 children. Each judge had more than 100 h of clinical experience and had completed a course in Phonetics before training commenced for this project. After discussion of the afore-mentioned characteristics of each misarticulation subtype, the group performed live voice judgments of four different children's /s/ errors (two retracters, one lateralizer, one dentalizer), until the group achieved an average agreement of

251

Delayed fs/ development TABLE II. Ratio of number of self-corrected vs. total number of subjects tested in a given school year for each of three subgroups of /s/ misarticulators (figures in parenthesis are percentages)

Age at start of school year (years)

Dentalizers Retracters Lateralizers

5

6

7

8/35 (23) 5/ 12 (42) 0/5 (0)

2/ 19(10) 2/4 (50) 0/4 (0)

3/ 14 (21) 2/3 (66) 0/5 (0)

90% over 25 successive productions for each child. During the experiment, on the third or fourth sampling session, two of the judges simultaneously judged an individual child, always achieving a joint agreement greater than 90%. The graduating judges were replaced by a new group who underwent the same training sequence.

2.3 . Data reduction

Each context was produced eight times during a particular test session, i.e. two repetitions of the four occurrences of each context in the sentence list. The judge assigned a score of correct (i .e. production of[s]) or incorrect (i.e. any non-[s] production). Correct production was calculated as a percentage for each context on each testing day. A total percentage correct for each day was also computed by averaging across the 16 contexts. The technique of Diedrich of Bangert ( 1980), for averaging adjacent testing dates via linear interpolation to common testing days, was adopted. Interpolations were performed between the test session preceding and the test session following each target day, i.e. Day 50, Day 100, Day 150 and Day 200.

3. Results 3. 1. Percentage of children mastering [s] production Children who exceeded 90% correct [s] production were judged to have achieved phonetic mastery of [s] production. Table II shows the number of children using each error allophone who reached mastery during each of the 3 years of the study. Overall, 22 children were observed to reach this criterion. Twelve children who were followed for 3 years failed to reach this criterion. The remaining 19 subjects were prematurely lost to the study over the 3 year period. Inspection of the 3-year totals for each error allophone reveals a strong effect of error allophone. Nearly all children who utilized a retracted [sr] production reached the criterion by the age of 7 years. Approximately half of the children who utilized a dentalized error mastered [s] production. No lateralizing children were observed to master [s] production. An interesting subgroup of four children utilized a dentalized [§]at age 5, but switched to a retracted [sr] by age 6. One of these children was lost due to subject attrition, but the other three eventually reached the criterion for self-correction.

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3.2. Individual subject growth

Figures 2 and 3 shows average percentage correct data for each subject in the retracting and dentalizing subject groups who mastered [s] production during the first year of the study. Subjects have been grouped by starting percentage correct (less than or greater than 50%). Development of [s] production by most of these children appears to be describable with a three stage pattern. In the first stage, an individual child maintains a relatively low percentage correct production. In the second stage there is an improvement in percentage correct production. This improvement phase appears to occur within 50 days for most of the children showing this pattern. The last phase may be a consolidation phase in which the child maintains a relatively high percentage correct [s] production while improving toward consistent correct production. This pattern is seen predominantly in the children whose percentage correct production starts out at below 50% correct. Approximately half of the children who start with percentages above 50% correct show relatively stable performance which may simply be a continuation of the S-shaped pattern described above. However, a number of children apparently diverge from this pattern by showing dramatic downward swings in their performance before mastery is attained. All of these children were seen to maintain their correct productions in the following school year, so it would appear that this stage of fluctuation is not indefinite in duration. 3.3. Phonetic context effects

Figure 4 shows the developmental patterns of the retracting and dentalizing children who developed correct articulation divided into Vowel and Consonantal contexts. Vowel contexts included those in which the fs/ was neither preceded nor followed by a consonant. Consonantal contexts included those in which either the sound preceding or following the /s/ was a consonant. These averaged data suggest no strong influence of the

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major class of the phones in immediate phonetic context. The patterns seen are indicative of the overall trends noted above for individuals. In general, the retracters started with higher percentage correct productions, but were more prone to decreases in correct production along the way. Figure 5 shows the percentage correct articulation for consonantal contexts divided according to place of articulation of either the preceding or following phone. The Labial average consists of the contexts in which [p] preceded or followed [s], the Alveolar average includes contexts in which [t] or [n] preceded or followed [s] and the Velar average included those contexts in which [k] preceded or followed [s]. There appears to be little influence of place of articulation of the context phones upon [s] development.

254

M. I. Stephens et a!. 4. Discussion

The present study sought to determine whether phonetic level mechanisms have an effect on delayed [s] development by 5-year-old children. Phonetic level phenomena studied included the type of phone utilized as a realization of jsj and the effect of immediate phonetic context upon development of jsj production. While the particular error allophone type produced by a child was strongly related to development of acceptable [s] production, phonetic contexts effects appeared to have little influence. All of the children who developed acceptable [s] articulation appeared to do so with a similar S-shaped growth pattern. All of the children in this study appear to have been in the stage of development in which a phonologically known fricative is represented by a fricative allophone judged to be phonetically non-standard by adults (Ingram et al., 1980). Results of the present investigation confirmed the primacy of the dentalized phonetic representation in this stage. The second most prevalent error sub-type seen in this study and others is a fricative produced with a place of articulation which is more retracted than usual. Several studies reported by Ingram eta!. (1980) found [f] and [t] to be the next most often utilized approximations of [s]. Labialization and Stopping are often reported as phonological processes employed by young children who misarticulate many phonemes (Ingram, 1976). Children in the present study did not utilize these error patterns, suggesting that they are in a group of children separate from those who utilize phonological processes. Lateralizing children may prove to be an exception to this hypothesized relationship. The children who produce lateralized fricatives may be dependent upon tractile cues indicating a central pathway constriction to guide their productions. Similar tactile targets may underly the use of stops rather than fricatives by children whose errors are described via the process of stopping. Indeed, Ladefoged (1971) maintains that air path is a manner feature, hence, lateralization may be a manner error, not unlike the stopping error utilized by children considered to be severely impaired in their articulatory development (Hodson & Paden, 1981 ). The persistence of the lateral fricative error demonstrated in this study leads one to suspect that these children differ from those producing other jsj error allophones, perhaps in some neuromuscular programming capacity. The relative coarticulatory in variance of this phonetic manifestation of jsj (Daniloff eta!., 1980) favors such an interpretation. However, Diedrich & Bangert (1980) reported that recovery from misarticulation during therapy was similar for dentalizing and lateralizing subjects, suggesting that neither allophone is more intransigent to therapeutically instigated change. In fact, all children who reached the age of 8 years with a persisting [s] misarticulation achieved mastery of [s] production within a few months of the onset of speech therapy. Phonetic context of [s] appeared to have little effect upon [s] production development (Fig. 5). Only one phonetic context, [sc], elicited a substantial increment of correct [s] production. Individual children improved their articulation but no particular consonantal, vocalic, or positional context appeared to differentially influence the rate of successful articulation of jsj, either within or across subgroups. Basically, scores of all contexts rose together as improvement progressed. Our results are congruent with those of Diedrich & Bangert (1980) who found no systematic effect of phonetic context on the course of therapy assisted development of jsj articulation. Our results and theirs suggest that contextual effects are rather idiosyncratic, are inconsistent across subjects and are

Delayed /sf development

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probably not as strong as lexical, syntactic or pragmatic factors may be in their influence on the learning of correct [s] allophones.

The authors wish to acknowledge the assistance of Mr. Roger Bastian, coordinator of speechlanguage- hearing services for pupils in the Rockford School System, Rockford, Illinois. This research was supported by a grant from NIH-NINCDS, grant No. IROIN515069.

References Daniloff, R. , Wilcox, K. & Stephens, M. (1980). An acoustic- articulatory description of children's defective /sf production, Journal of Communication Disorders, 15, 347- 363. Diedrich, W. & Bangert, J. (1980). Articulation learning. Houston: College-Hill Press. Gallagher, T. & Shriner, T. (1975) . Articulatory inconsistencies in the speech of normal children, Journal of Speech and Hearing Research, 18, 623- 633 . Hardcastle, W. (1976). Physiology of speech production . New York: Academic Press. Haynes, W., Haynes, M. & Jackson, J. (1982). The effects of phonetic context and linguistic complexity on /sf misarticulation in children, Journal of Communication Disorders, 15, 287- 298 . Hodson, B. & Paden, E. (1981). Phonological processes which characterize unintelligible and intelligible speech in early childhood, Journal of Speech and Hearing Disorders, 46, 369- 373. Ingram, D. (1976). Phonological disability in children . New York: American Elsevier Press. Ingram, D., Christman, L., Veach, S. & Webster, B. (1980). The acquisition of word-initial fricatives and affricates in English by children between 2 and 6 years. In Child phonology volume 2 (G. YeniKomshian, J. Kavanaugh & C. Ferguson, editors). New York: Academic Press. Kent, R. & Moll, K. (1972). Cinefluorographic analysis of selected lingual consonants, Journal of Speech and Hearing Research, 15, 453- 473 . Ladefoged, P. (1971). Preliminaries to linguistic phonetics. Chicago: University of Chicago Press. Mazza, P. , Schuckers, G. & Daniloff, R. (1979). Contextual-{;oarticulatory inconsistency of fs/ misarticulation, Journal of Phonetics, 7, 57-69. Oller, D . & MacNeilage, P. (1983). Development of speech production: perspectives from natural and perturbed speech . In Speech production (P. MacNeilage, editor). New York: Springer-Verlag. Prather, E., Hedrick, D . & Kern, C. (1975). Articulation development in children from two to four years, Journal of Speech and Hearing Disorders, 40, 179- 191.

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Snow, K. (1963). A detailed analysis of articulation responses of normal first grade children, Speech Monographs, 31, 135- 141. Spriestersbach, D. & Curtis, J. (1951) . Misarticulation and discrimination of speech sound, Quarterly Journal of Speech, 37, 483- 489. Subtelny, J., Oya, N. & Subtelny, J. (1972). Cineradiographic study of sibilants, Folia Phonetica, 24, 30- 50. Templin, M . (1957) . Certain language skills in children: their development and interrelationships. Institute of Child Welfare Monograph 20. Minneapolis: The University of Minnesota Press. Wood, S. (1979). A radiographic analysis of constriction location for vowels, Journal of Phonetics, 7, 25- 43 .