the motor planning abilities of phonologically disordered children

European Journal of Disorders of Communication, 29,349-369,1994 0 College of Speech and Lmguage Therapists, London

349

The motor planning disordered children

abilities of phonologically

Amanda Bradford and Barbara Dodd Department of Speech and Hearing, University of Queensland, Australia

ABSTRACTS The motor planning abilities of three subgroups of speech-disordered children were compared to normally speaking age- and comprehension-matched controls. There were 10 phonologically delayed children who used sound-pattern errors typical of chronologically aged younger children (delayed group); 10 children whose phonological system was characterised by the consistent use of non-developmental phonological processes (deviant consistent group); and 10 children whose production of specific lexical items and phonological features was variable (inconsistent group). The groups were compared on ’tasks that assessed simple and complex motor planning for hand movements and expressive and receptive novel-word learning. The groups did not differ on a simple task of motor planning for hand movements. However, the inconsistent group performed more poorly than all the other groups on a more complex, timed motor-planning task. Although the groups performed equally well on a task assessing receptive novel-word learning, the inconsistent group performed more,poorly than all the other groups on an expressive novel-word learning task. The results provide support for the hypothesis that speech-disordered children with different surface error patterns have different underlying deficits in the speech-processing chain. Specifically, inconsistent error patterns are associated with a deficit in some aspects of fine motor planning.

La capacitk de programmation motrice de 3 sous-groupes d’enfants ayant des troubles de la parole a ktk comparte d celle de groupes de contr8le d‘enfants normaux, apparillts selon l‘dge et la com- prthenswn: 10 enfants retardts sur le plan phonologique utilisaient les erreurs phoniques typiques des enfants normaux plus jeunes (groupe ‘retardks’); I0 enfants dont le systime phonologique ttait caracterisd par l‘emploi cohtrent de processus phonologiques non-dtveloppementaux (groupe ‘dkviants cohkrents’); enfin I0 enfants dont la production #items lexicaux specifiques et de traits phonologiques ttait variable (groupe ‘non-cohtrents’). Les groupes ont kt6 comparks d‘aprRr des aches qui tvaluaient la programmation motrice simple et complexe pour les mouvements de la main ainsi que pour l‘apprentissage de mots nouveaux sur les plans expressif et recepti6 I1 n’y a pas eu de diffkrence pour les tdches simples de programmation motrice des mouvements de la main. Cependant, le groupe non-cohtrent a exkcutk d’une mani2i-e plus faible que tous les autres groupes les tdches plus complexes de programmation motrice avec contrainte de vitesse. Alors que les groupes ont eu le m8me bon comportementpour les tdches d’kvaluation de l‘apprentissage des mots nouveaux sur le plan receptif; le groupe %on-cohtrents’ a eu des rksultats bien plus faibles pour les tdches d’apprentissage de mots nouveaux sur le plan expressif: Ces rtsultats contribuent d renforcer l‘hypothbe que les enfants ayant des troubles de la parole se manifestant par des erreurs de surfme difftrentes ont des dkficits sow-jacents tout le long du processus de parole. D’une munCre sptci- fique, les types d’erreurs non-cohtrentes sont associks avec un ddficit de certains aspects de la programmation motrice fine.

Die motorische Planung dreier Untergruppen sprachgestbrter Kinder wurde rnit normalsprechen- den Kontrollgruppen verglichen, die ihnen im Sprechalter und Sprachverstehen entsprachen. Die Untergruppen waren: 10 Kinder mit verzbgerter phonologhcher Entwicklung, die Fehler in den

350 BRADFORD AND DODD

lautlichen Mustern aufwiesen, die fur chronologisch jiingere Kinder typisch sind (verzogerte Gruppe); 10 Kinder, deren phonologisches System durch die konsistente Veiwendung von in nor- malen Entwicklungsstufen nicht vorkommenden phonologischen Prozessen charakterisiert war (abweichende Gruppe); 10 Kinder, deren Produktion bestimmter lexikalischer Formen und phonol- ogischer Merkmale variabel war (inkonsistente Gruppe). Die Gruppen wurden bei Aufgaben verglichen, die die Evaluierung a) einfacher und komplexer motorischer Planung fur Handbewegungen und b) expressiver und rezeptiver Erlernung neuer Worter ermoglichten. Die Gruppen unterschieden sich bei der einfachen motohchen Planung nicht, aber bei der komplex- eren, zeitkontrollierten motorischen Planungsaufgabe war die Leistung der inkonsistenten Gruppe schlechter als die der anderen. Wdhrend alle Gruppen bei der rezeptiven Erlernung neuer Worter gleich gut waren, war die inkonsistente Gruppe bei der expressiven Erlernung neuer Worter wiederum schlechter als alle anderen Gruppen. Die Ergebnisse unterstiitzen die Hypothese, dafi sprechbehinderte Kinder mit unterschiedlichen Obe rflichenfehlern auch unterschiedliche zugrun- deliegende Schwachen der Sprachverarbeitungskette haben. Insbesondere treten inkonsistente Fehlermuster in Verbindung mit Schwachen in einigen Aspekten der feinmotorischen Planung auf.

Key words: phonological disorder, motor planning abilities.

INTRODUCTION Estimates of the incidence of developmental speech disorder range from 3% to 10% of the normal school population (Enderby & Philipp, 1986). It is the most common communication disorder in childhood because almost 70% of children attending paediatric clinics are speech disordered (Weiss, Gordon & Lillywhite, 1987). However, these children are not a homogeneous group: they differ in terms of the severity of the disorder, implicated aetiological factors, type of surface speech-sound error patterns made and response to different treatment approaches (Dodd, 1993). Although the need to class@ subtypes of speech disorder is generally agreed (McNutt & Hamayan, 1982), how best to categorise speech-disordered children into subgroups remains controversial. One approach has been to class@ children in terms of the aetiological factors that might underlie their speech disorder (Shriberg, 1982). Organic deficits such as cleft palate, cerebral palsy (Winitz & Darley, 1980) and hearing loss (Silverman & Calvert, 1978) are obviously associated with impaired speech production. However, the proportion of children referred for assessment of a speech disorder who have craniofacial anomalies, dysarthria or currently impaired hearing is small. Consequently, to account for most of the children who present with no obvious organic aetiology, researchers have sought links between speech disorder and other abilities thought to be prerequisites for normal phonological acquisition.

Input Deficits It is a common assumption that children make speech errors because they have misperceived adult speech. Many phonologically disordered children have a history of otitis media which may be associated with periods of hearing loss, Hearing loss during infancy may impair their learning of their native language’s system of phonemic contrasts (Kirkwood & Kirkwood, 1983). Hearing loss during early childhood might impair auditory discrimination leading to the lay- ing down of incorrect or incomplete mental representations of words that may not be corrected when normal hearing is restored (Katz & Illmer, 1972). How- ever, the evidence concerning a causal link between episodes of otitis media and phonological disorders is far from clear-cut. Most children (75%) experi-

PHONOLOGICALLY DISORDERED CHILDREN 35 1

ence at least one episode of otitis media with effusion (OME), and well over 10% will have recurrent episodes (Teele, Klein & Rosner, 1984). Not all these children become phonologically disordered. Prospective studies of subjects enrolled in early infancy suggest that although fluctuating hearing loss may be a contributing factor to phonological disorder, it is rarely the sole cause (Teele et al., 1984; Wright, Sell, McConnell, Sutton, Thompson, Vaughan & Bess, 1988).

In the absence of any current or past history of sensory impairment, central auditory processing impairments are often cited as a major cause of phonological disorders (Sommers, 1984; Tallal, 1987). Some speech-disordered children do perform poorly on tasks assessing auditory discrimination, perception and processing (Tallal & Piercy, 1973; Tyler, Edwards & Saxman, 1990; Bird & Bishop, 1992). However, not all children in the groups tested were shown to have impaired input processing and Dodd and Basset (1987) found that their phonologically disordered subjects were able to process language receptively as rapidly and accurately as normal peers. Katz (1983) reviewed the literature concerning the relationship between speech disorders and phonemic synthesis (the ability to ‘blend’ distorted speech sounds into words). He concluded that those speech-disordered children who performed more poorly than age- matched controls had a wide range of impairments, including receptive language, attention and memory. There is, then, little evidence for central auditory processing deficits being a cause of phonological disorders in the absence of more general learning disability.

General Linguistic Deficit Other researchers have argued that children who are phonologically disordered have a general language learning disability. Some studies suggest that they have deficits in symbol acquisition per se (Steig Pearse, Dawish & Gaines, 1987), and that they perform poorly on measures of other aspects of spoken language, i.e. grammar and semantics (Winitz & Darley, 1980; Steig Pearse et al., 1987). Other studies have found no group differences between speech-disordered and control groups on language screening measures (Lewis & Free- bairn, 1992). However, although many children who have a phonological difficulty also perform poorly on standardised assessments of other language abilities, this does not necessarily mean that they have multiple underlying deficits for the three different aspects of language: phonology, syntax and semantics (see Reed, 1992, for review). Rather, phonological disorder may influence performance on tests of syntax and semantics. For example, many children with a phonological disorder delete word final consonants so that they pronounce ‘bats’ as [bz], ‘played’ as [ple~] and ‘cats’ as [kz], i.e. the phonological process of final consonant deletion influences the child’s ability to mark plurality, tense and possession syntactically.

Obviously this affects how well they score on tests of morpheme use. Fur- ther, phonologically disordered children may use strategies to enhance their intelligibility: primarily the use of short utterance (affecting measures of mean length of utterance) and the use of generic, rather than specific terms (e.g. man rather than policeman; flower rather than rose, in spite of being able to identify pictures when given specific names), influencing measures of expressive vocab-

352 BRADFORDANDDODD

ulary (Brierly, 1987). Consequently, studies claiming that phonological disorder is often just one symptom of a general language learning disability must be viewed with caution.

Motor Deficit Another important strand of research into deficits underlying speech disorders has focused on motor ability. A number of studies have supported the hypothesis that speech-disordered children have associated impaired motor skills (Cer- mak, Ward & Ward, 1986; Sommers, 1988; Carroll, Fuller & Lindley, 1989) as assessed by tasks measuring motor coordination, fine motor skills and visuo- motor skills. In contrast, other researchers have concluded that the link is tenu- ous (Kornse, Manni, Rubenstein & Graziani, 1981; Aram & Horwitz, 1983; Lewis, Ekelman & Aram, 1989). The results of these studies found little evidence of motor impairment when speech-disordered children, including some diagnosed as dyspraxic, were assessed using measures of gross and fine motor function (e.g. dexterity, manual gestures, constructional tasks). Again the results are contradictory, some groups of speech-disordered children performing poorly on some motor skill assessment tasks.

Classification of Subtypes of Phonological Disorder Reviews of research that has sought to identify the deficits underlying speech disorders usually stress that conflicting findings are the rule rather than the exception (e.g. Winitz, 1969; Sommers, 1984). These contradictory findings can be attributed to two factors: methodology and population sampling.

Methodology Researchers employ widely differing methodologies to assess candidate pre- requisite skills. The same group of children could be considered to be performing within normal limits or to have a specific deficit in a particular skill, depending on how the skill under investigation was assessed. For example, when Bountress (1984) compared the results of a single group of non-communication-disordered children on three different standard assessments of speech perception, he found statistically significant differences in performance among the tests. One obvious source of conflicting results is, then, that studies that have focused on auditory processing, linguistic abilities and motor skills have used tasks that have assessed different aspects of complex mental processes.

Population sampling Many studies have assumed, incorrectly, that speech-disordered children are a homogeneous population. Thus different populations of speech-disordered children have varied in their performance on identical tasks. Speech-disordered children vary in terms of the severity of their disorder and the type of errors made: a child whose speech disorder is restricted to a problem in articulating /s/ (a lisp) is considerably less impaired than those who make multiple speech sound errors; and a child whose error pattern reflects delayed development dif- fers from one who uses non-developmental phonological rules, e.g. marking all syllable initial fricatives and affricates with /hh deleting all word initial conso-

PHONOLOGICALLY DISORDERED CHILDREN 353

nants. It is, then, hardly surprising that studies using heterogeneous populations of speech-disordered children produce conflicting findings. Inconsisten- cies in previous research would indicate the need to identify subgroups of speech-disordered children.

As most speech disorders are considered to be ‘functional’, i.e. to have no established organic cause (Sommers, 1984), classrfying children into subgroups according to identifiable aetiological factors is difficult. An alternative approach is to classrfy subgroups of speech-disordered children according to linguistic typologies. However, the first research studies investigating classification systems based on linguistic typologies yielded little information. Both Arndt, Shelton, Johnson and Furr (1977) and Winitz and Darley (1980) tested large groups of children seeking associations between speech error patterns and independent variables, such as measures of language, motor skills, auditory discrimination and oral stereognosis. No reliable associations were found. One plausible explanation for this failure to find any relationship between types of errors and other speech-related abilities is that the linguistic typologies employed focused on speech sounds rather than phonological processes. Dodd’s (1993) review identified three linguistic typologies based on phonological process use that have emerged in the description of what constitutes phonological disorder: 1. Delay (Fletcher, 1990). 2. Consistent but unusual (non-developmental) phonological errors (Leonard,

3. Inconsistent phonological errors (Dodd & Leahy, 1989).

Perhaps these three categories may reflect the nature of the deficits underlying subgroups of phonologically disordered children.

Dodd, Leahy and Hambly (1989) tested this possibility by comparing the performance of three groups of subjects, selected according to the nature of their surface phonological errors:

Children using normal developmental processes that were inappropriate for their chronological age - ‘delayed’. Children using some consistent but non-developmental processes - ‘deviant consistent’. Children who exhibited many apparently non-rule governed errors - ‘deviant inconsistent’.

In one experiment their production errors in imitation, picture naming and spontaneous speech were evaluated. The results distinguished between the three subgroups of phonologically disordered children, providing an initial validation of the classification. The delayed group made fewer errors than the other two groups but had stable performance across the three production tasks. The deviant consistent group’s errors increased with the linguistic complexity of the production task, e.g. better production of a word in isolation than in connected speech (Leahy & Dodd, 1987). The inconsistent group were better in imitation than in elicited or spontaneous production.

Other experiments comparing these three subgroups of phonological disorder

1985).


have revealed that the deviant consistent group perform poorly on tasks involving detection of phonological legality of spoken nonsense words, recognition of their own phonological forms (Dodd et al., 1989), and awareness of alliteration and rhyme (Brierly, 1987). These findings suggest that the use of consistent but unusual phonological rules might be attributed to an impaired ability to abstract knowledge from the mental lexicon about the nature of the phonological system to be acquired. Leonard (1985) views children as active learners of their phonological system, who seek to mark, in their speech output, the contrasts that they perceive between words. Consistent but bizarre solutions to the problem of marking differences might result from selecting the wrong parameters of the perceived speech signal as salient in their native phonology. If this were so, these children’s deficit could be labelled cognitive and lie in Grundy’s (1989) organisational level of the speech chain.

Both the phonologically delayed and inconsistent groups appeared to have unimpaired metaphonological abilities, performing similarly to controls on the tasks that distinguished the deviant consistent subgroup (Brierly, 1987; Dodd et al., 1989). Although phonological delay can be generally accounted for in terms of an impoverished language learning environment or slow neurological maturation (Dodd, 1993), deviant inconsistent errors would seem to be associated with a more specific deficit. Variability of pronunciation of particular words or phonological features (e.g. clusters) is considered to be one diagnostic indicator of developmental verbal dyspraxia (DVD), a disorder of motor planning (Crary & Towne, 1984; Dewy, Roy, Square-Storer & Hayden, 1988; Stackhouse & Snowling, 1992). However, many children who make inconsistent errors do not present with other behaviours thought to be part of the symptom cluster necessary for the diagnosis of DVD, including: trial and error articulatory groping; poor performance on diadochokinetic tasks; disruption of the volitional production of phonemes; and, an increased number of errors with increased length of utterance (Ozanne, 1992). There may be, then, a subgroup of phonologically disordered children whose speech is characterised by inconsistent errors who, although not meeting all the criteria for diagnosis of DVD, have a deficit in motor planning.

There is a long-standing debate in the literature on the nature of motor control of skilled actions. Some theorists assert that execution of a skilled motor act has multilevel involvement from higher cognitive or cerebral functions (e.g. Semjen & Gottsdanker, 1992; Shaffer, 1992; Soumi, 1993), whereas others suggest that peripheral systems of muscle groups coordinate and interact to organise movement for invariant goals (Fowler, Rubin, Remez & Turvey, 1980; Kelso, 1981). As lexical and syntactic processing demands influence speech production, motor planning for speech must be mediated, to some extent, by a motor control system outside the peripheral muscle group. As Shaffer (1992, p. 181) stated:

To get from intention to sound, the brain must form a symbolic representation, with appropriate syntax, of the semantic entity, and translate this into a pattern of movement involving the respiratory system and vocal tract. The muscles effecting movement know nothing about natural language or its meaning and must be instructed what to do in muscle language.

That is, motor planning refers to the mental processes that derive precise artic-


ulatory instructions for the pronunciation of a word from an abstract phonological representation.

The primary aim of the investigation reported here was to examine the performance of subgroups of phonologically disordered children on motor planning tasks that tapped different levels of complexity. The three groups of speech-disordered children assessed were those with delayed phonological development, those who consistently used at least two non-developmental phonological processes and those who made inconsistent errors. The tasks selected tapped the ability to perform a simple repetitive manual motor act, a standardised manual motor accuracy test involving a more complex motor act, and a task assessing children’s ability to learn to pronounce novel words - a task requiring extremely complex fine motor planning. It was hypothesised that the deviant inconsistent group would perform more poorly than all other groups on all tasks. If children whose pronunciation of words is unpredictable (because they produce a number of different realisations of a single lexical item) have a generally impaired ability to formulate correct motor plans for fine motor acts, then they should perform poorly on both manual and articulatory tasks.

METHOD Subjects Thirty phonologically impaired children participated in the study. These children were referred to the investigation by speech pathologists from a major public hospital and from education department clinics in a metropolitan area, and were either on waiting lists for treatment or currently receiving therapy. Subjects’ ages ranged from 3;3 years to 6;8 years, with a mean age of 4;9 years (Table 1). There were six girls and 24 boys in the experimental groups. Criteria for participation in the study were: 1. Language comprehension skills within normal limits for chronological age,

as assessed by the child’s speech pathologist using a standardised comprehension assessment such as Reynell Developmental Language Scale - Revised (Reynell, 1977) or Test for Auditory Comprehension of Language - Revised (Carrow-Woolfolk, 1985).

2. No known neurological or physical cause of speech impairment (ag. children with dysarthria or craniofacial anomalies were excluded).

3. No evidence of a history of middle-ear infections or sensorineural hearing loss.

4. No diagnosed visual or visual perceptual deficits. 5. Australian English was the only language spoken at home. 6. Presence of a phonological impairment, as diagnosed by the child’ s speech

pathologist. 7. Absence of salient diagnostic features of developmental verbal dyspraxia

(Murdoch, Porter, Younger & Ozanne, 1984). The 30 children in the normal control group were drawn from the same

schools as the experimental subjects to control for socioeconomic status. Parti- cipants in the investigation were classified as having low-middle socioeconomic status, based on their parents’ occupations The age range of children in the


control group was 3;2-6;6 years, with a mean age of 4;9 years. The group included 11 girls and 19 boys. To be assessed as a control, a child had to meet the following criteria: 1. Normal speech and language skills as judged by the investigator in an infor-

mal play session. 2. No history of past speech and language impairment. 3. No reported history of academic difficulties.

Control children were matched pairwise with phonologically disordered subjects for age, gender and hand preference. All children’s parents signed a con- sent form and were invited to attend the assessment session.

Procedure Children were assessed in a single session, either at their Speech Therapy Clinic, or a quiet room at home or school. The session consisted of a period of free play to allow the examiner to gain rapport with the child and elicit a connected speech sample from speech-impaired subjects. The experimental tasks were administered in the same order for each subject.

Group assignment lkenty minutes of connected speech, gathered from phonologically impaired subjects during the initial play session, were recorded using a JVC Portable Stereo Cassette Deck (KD-1635 Mark 111) with an external microphone. A broad transcription of the recorded sample was completed by the examiner following the assessment session, using the revised edition of the International Phonetic Alphabet, with diacritics where necessary. A second speech pathologist, experienced at transcribing disordered speech, retranscribed six randomly selected speech samples. Inter-rater reliability of transcription was 96%.

Group assignment was carried out independently by two speech pathologists on the basis of phonological process usage in the connected speech sample. Phonological processes were classified as either delayed or deviant (see Appendix I). Children were assigned to three experimental groups: (1) delayed phonology, (2) deviant consistent phonology and (3) deviant inconsistent phonology (see Appendix I1 for criteria on group assignment and Appendix I11 for examples of the errors of children classified as belonging to different groups). There were two disagreements over group assignment (between deviant inconsistent and consistent); these were discussed and settled following input from a third speech pathologist. The age and number of subjects in each group are shown in Table 1.

Task 1: Peg-board Task Aim To assess speed and accuracy of simple repetitive hand movements.

Materials The peg-board consisted of an 8 x 5 matrix of equidistant holes in a wooden board. At their widest point, the pegs measured 14mm in diameter, with a shaft 7 mm in diameter.


Table 1 : Age and number of subjects

Number of subjects aged Mean age in

Group months (s.d.) 3years 4years Syears 6years Total ~~ ~~

Control 57.4 (11.7) 7 9 10 4 30 Delayed 60.8 (11.8) 1 5 2 2 10 Consistent 54.2 (9.5) 2 5 3 0 10 Inconsistent 55.3 (13.3) 3 4 1 2 10

Totals 56.9 13 23 16 8 60

Procedure Pegs were initially arranged in the peg-board so that there were six rows of five pegs, then one row of unfilled holes, then one row of five pegs. The child was seated at a table of appropriate height, and instructed to move the 30 pegs up one row to meet the five distant pegs, as fast as he or she could. Only the preferred hand was used. A demonstration was provided if necessary. The time taken to move the 30 pegs yielded the score for this task.

Task 2: Motor Accuracy Test - Revised Aim To assess the ability to establish and execute complex motor plans to allow accurate tracing using pen and paper.

Materials The Motor Accuracy Test - Revised (Ayres, 1980) was employed for this task. This is a standardised assessment which requires children to trace around a closed shape, printed on a 419 mm x 295 mm page, using a red ball point pen of medium density. A pedometer was used to measure tracing error.

Procedure Standardised procedures and instructions were used in administra- tion of the test (see Ayres, 1980, for details). Children were seated at a table of appropriate height and told that the aim of the game was to draw on the black line using a red pen. Only performance of the preferred hand (as reported by a significant other) was measured. The task was demonstrated, and the child had one trial before the test proper. The examiner’s finger indicated the appropriate path to trace, and the child was cued as to how fast to go to complete the task in 60 s. One minute was chosen as the performance time because it is the most reliable indicator of motor accuracy (Ayres, 1980). The standardised scoring procedure was adhered to to obtain a standard score for each child. The motor accuracy score represents the length of line that the child’s line falls between measured distances either side of the line to be traced. A pedometer was used for line measurements. The motor-adjusted score was the motor accuracy of the child’s performance as a function of time. As normative data for children of 3 years of age were not available in the scoring manual (Ayres, 1980), the mean and standard deviation of scores obtained by control subjects (aged 3;2-3;11 years) were used to derive standard scores for the youngest phonologically disordered subjects.


Task 3: novel word learning Aim To assess the ability to generate and execute motor plans for the articulation of novel words.

Materials An attractively illustrated book, depicting the story of ‘The Three Little Pigs,’ was used. Each pig was given a name that was a disyllabic novel word which adhered to the phonotactic constraints of English ([pa~zi], [Jilak], [ne~dal]). Names for fictional characters were chosen as stimuli to avoid con- founding effects of trying to teach children novel names for objects with which they were familiar (e. g. Brierley, 1987). To further differentiate between the pigs, an additional distinctive feature was added to each picture of the pig (e.g. glasses, a tie, a hat). Each pig was portrayed 10 times throughout the book, generating a total of 30 presentations of the stimulus words.

Procedure It was explained to the subjects that they would learn the names of the ‘Three Little Pigs’. The child was then shown the picture book, and the names of the pigs were introduced in combination with the distinctive feature of each character. The story was then told to the child, with the name of each pig mentioned 10 times throughout the presentation. Presentation of the task in a story-book format was chosen to maximise interest and motivational factors and to provide a context for the test words, because children rarely learn lexical items out of context. The child was encouraged to imitate the test words during the presentation and, following completion of the story, the tester sug- gested that it was the child’s turn to tell the story. Production of each test word was elicited five times, by cues such as ‘What was his name?’. Responses were immediately transcribed, and scored at the completion of the session. Correct responses (and errors that were a stable part of the child’s phonological system) scored 3 points, incorrect but close approximations, 2 points, 1 point for imitation, and 0 points for no response, an unrecognisable attempt or lexical mismatch.

Scores for each test word were summed to yield an expressive score, which was converted into a percentage score.

An additional measure for each child was derived from the imitation data. The number of correct imitations of the novel words was expressed as a percentage of the total number of imitative attempts. This measure was calculated to control for: 1. Word retrieval difficulties: poor performance on this task might reflect diffi-

culty in recalling the names of particular pigs, rather than an impaired memory for how to say their names. Imitation is a pure measure of the articulation of the target words.

2. The procedure for calculating the expressive score disadvantaging children making inconsistent errors as opposed to consistent errors. If children in the inconsistent group produce fewer totally correct imitated versions of the adult forms than the other groups, then their deficit in novel word production would not just be an artefact of the scoring procedure used to derive the expressive score.

In the comprehension task children were asked to point to named characters.


Each test word was presented three times in a random order. The measure was the number of correct identifications, converted to a percentage score.

RESULTS

Age of Subjects A single-factor analysis of variance (ANOVA) indicated no significant difference between the groups term with respect to age (F = 0.63; d.f. = 3’56; p = 0.60). Age means and standard deviations for the groups are shown in Table 1.

Table 1 : Age and number of subjects

Number of subjects aged

Group Meanagein 3years 4years 5years 6years Total months (sd.)

Control 57.4 (11.7) 7 9 10 4 30 Delayed 60.8 (11.8) 1 5 2 2 10 Consistent 54.2 (9.5) 2 5 3 0 10 Inconsistent 55.3 (13.3) 3 4 1 2 10

Totals 56.9 13 23 16 8 60

Task 1: Peg-board Task Scores for this task consisted of time (in seconds) taken to move 30 pegs from one hole to an adjacent hole (Table 2). A one-factor analysis of variance comparing the four groups’ performance was not significant (F = 2.33; d.f. = 3’56; p = 0.084), i.e. the groups performed equally on this simple motor planning task.

Table 2: Peg-board task: time taken to move 30 pegs

Group Mean time (s) taken Standard deviation to move 30 pegs

Control 45.6 Delayed 45.7 Consistent 55.6 Inconsistent 56.9

11.9 163 14.1 19.2

Task 2: Motor Accuracy Test - Revised This test yielded standard scores for motor accuracy and motor adjustment (accuracy corrected for the time taken to complete the task) for each subject. The means are shown in Table 3. Two of the children in the inconsistent group’s tracing did not approximate the target shape sufficiently to allow for reliable scoring, in spite of serious attempts. These two children were awarded scores that were equal to the child in the inconsistent group who performed most poorly. The measures were considered separately in two single-factor analyses of variance (group x score).


Motor accuracy score The analysis of variance showed a significant groups’ difference (F = 6.918; d.f = 3, 56; p = 0.001). Post-hoc tests using Fisher’s Least Significant Difference Test (Wilkinson, 1987) indicated that the inconsistent group performed more poorly than the control group (p < 0.001), the delayed group (p = 0.001) and the deviant consistent group (p c 0.01). No other pairwise comparisons were significant, i.e. the control, delayed and deviant consistent group performed equally well.

Table 3: Mean (s.d.) motor accuracy and motor-adjusted scores

Motor accuracy Motor adjusted ~~

Control -0.10 (0.62) -0.17 (0.7) Delayed -0.10 (0.40) 0.03 (0.18) Consistent -0.44 (0.64) -0.59 (0.75) Inconsistent -1.55 (1.79) -1.78 (1.99)

Motor adjusted score The analysis of variance was significant (F = 7.368; d.f. 3, 56; p < 0.001). Post- hoc tests using Fisher’s Least Significant Difference Test (Wilkinson, 1987) indicated that the inconsistent group performed more poorly than the control group (p c 0.001), the delayed group (p < 0.001) and the deviant consistent group (at p c 0.025). No other pairwise comparisons were significant, i.e. the control, delayed and deviant consistent group performed equally well.

Task 3: Novel Word Learning Expressive and receptive percentage scores were considered separately in two single-factor analyses of variance. The consistent deviant and inconsistent groups’ ability to imitate the novel words was compared using an independent t-test. The means and standard deviations are shown in Table 4.

Novel word expressive task The analysis was significant (F = 8.271, d.f. = 3, 56; p c 0.001). Post-hoc tests using Fisher’s Least Significant Difference Test (Wilkinson, 1987) indicated that the inconsistent group performed more poorly than the control group (at p c 0.001), the delayed group (at p = 0.025) and the deviant consistent group

Table 4: Novel word learning: expressive and receptive mean percentage scores (s.d.)

Group Imitation: 90 correct Expressive score+ Receptive score

Control %.O (16.5) 62.7 (16.4) 72.0 (30.0) Delayed 88.9 (33.3) 53.1 (16.0) 80.2 (19.9) Consistent 62.1 (29.8) 50.5 (11.0) 76.9 (18.3) Inconsistent 21.0 (23.8) 37.0 (9.6) 59.0 (23.6)

*Correct response scored 3 points; incorrect but close approximations, 2 points; 1 point for imitation; and 0 points for no response.

PHONOLOGICALLY DISORDERED CHILDREN 36 1

(at p c 0.05). No other painvise comparisons were significant, i.e. the control, delayed and deviant consistent group performed equally well.

When children in the control group imitated the novel words, 26 of them made no errors of pronunciation and eight of the children in the delayed group also rendered perfect imitations, resulting in a ceiling effect. Consequently, the results of the inconsistent and consistent groups were compared using an independent t-test, which was significant (t(9) = 2.952, p < 0.025). Inspection of the means (Table 4) shows that the inconsistent group imitated fewer of the novel words totally correctly than the consistent deviant group.

Novel word receptive task There was no difference between the performance of the groups on this task (F = 1.273; d.f. = 3,56; p = 0.287), i.e. the groups performed equally when asked to identify a character with a novel name following several presentations of the test word.

DISCUSSION Three groups of speech-disordered children (delayed, deviant consistent and inconsistent) and normally speaking controls were assessed on a simple motor programming task (peg-board), a more complex motor planning task (Ayres, 1980) and a novel word learning task (receptive and expressive). It was hypothesised that the deficit underlying the inconsistent group’s speech disorder was one of motor planning and that they would therefore perform more poorly than the other speech-disordered and control groups on all the motor planning tasks. The results indicated that the groups did not differ on the simple motor planning task that measured the time taken to move 30 pegs from one hole to another. However, the inconsistent group performed more poorly than all the other groups on tasks assessing complex manual motor planning (tracing a shape) and expressive novel word learning (establishing a motor plan for articulation), whereas the delayed and deviant consistent groups did not differ from one another or the control group on these tasks. Each of the tasks will now be discussed in more detail.

Peg-board Task Using a similar task, Kornse et al. (1981) reported that females with developmental verbal dyspraxia moved significantly fewer pegs in a specified time than did control subjects. In contrast, the results of the experiment reported here found no difference between the groups in terms of the time taken to move 30 pegs from one hole to another. The difference between the studies’ findings may reflect the different subject groups assessed. Children with developmental verbal dyspraxia may have a more significant motor planning deficit, i.e. appar- ent even in a simple repetitive motor task, than children who make inconsistent errors but evidence no other signs of dyspraxia. Although there was a trend for both the deviant consistent and inconsistent groups to perform poorly, their group means being about 10 seconds slower than those of the delayed and control groups, the large individual differences between subjects within groups resulted in a lack of statistically significant difference. One plausible explanation for the failure of the inconsistent group to differ from the other groups is

362 BRADFORDANDDODD

that the peg-board task may not have been complex enough to elicit a clear cut-off between the groups.

Motor Accuracy Test - Revised The Motor Accuracy Test (Ayres, 1980) is a more difficult motor planning task requiring coordination of spatial programming and fine kinaesthetic and visual error detection (Laszlo & Bairstow, 1985). The subjects in the inconsistent group performed more poorly than the control and other speech-disordered groups. Although the children in the inconsistent group were able to maintain adequate pencil grip and trace on some parts of the figure, overall their tracing was less accurate than other subjects, i.e. their tracing attempts were further from the target line. The motor adjusted score, which incorporated a time-cor- rection factor, showed an increased gap between the inconsistent group (who performed most poorly) and the deviant consistent group (the next worst group). Timing is a crucial element in speech motor planning and thus this task is a closer analogy for the complexities of speech production. That the inconsistent children had significantly more difficulty on this task as compared to the other groups suggests that, although their overall dexterity and precision of fine movements is not seriously impaired (as shown in the pegboard task), their ability to organise complex sequences of movement with respect to time is significantly impaired.

Novel Word Learning The groups did not differ statistically in their ability to learn novel words receptively, suggesting that children understood the task and that their production errors did not reflect unstable or incomplete internal mental representations of the words. However, the non-significant statistical finding may have resulted from the large standard deviations found for all groups. The inconsistent group’s lower mean score for the receptive task may indicate that more children in that group had difficulty establishing mental representations of the novel words. Nevertheless, the non-significant result supports Hughes’ (1983) conclusion that children’s internal representations of words are more like the adult (input) forms than their surface production errors. Further, Bird and Bishop (1992) concluded that, although some phonologically impaired children evidenced perceptual difficulties, these were not significant enough to explain their production deficits.

The results from the expressive section of this task revealed that children in the inconsistent group were less able to produce novel words than the other groups, who did not differ in their ability to produce the novel words. These results conflict with those of Brierley (1987), who found that speech-disordered subgroups did not differ on a similar task, although normal children were significantly better than speech-impaired subjects. These conflicting findings may be attributed to methodological differences. The current investigation tested learning of only three words (in comparison to Brierley’s five words), reducing the memory load. Also, the presentation context - names for the three little pigs in a familiar story-telling task - was more natural than context-free presentation of five new real words. Also, Brierley (1987) used unfamiliar real words (e.g. rickshaw) that children may have associated with a more generic


term (e.g. cart). The use of novel word names for familiar story characters would have circumvented any lexical interference. Perhaps the use of novel words in this investigation better reflected the inconsistent group’s difficulty with novel word production, because they were unable to avoid the task by using semantically appropriate lexical substitutions.

The finding that the inconsistent group performed more poorly than the other two phonologically disordered groups (deviant consistent and phonologically delayed) on the novel name learning task may be explained in a number of ways: 1. The finding might reflect the scoring procedure used. Errors that were a

consistent part of the child’s system were awarded more points than those that had not been found to be a result of a pattern used in the initial transcribed conversation sample. Thus children in the delayed and deviant consistent groups, who made consistent errors, might have scored more highly than children who made inconsistent errors. However, children in the inconsistent group produced fewer totally correct imitated versions of the adult forms than the other groups (see Table 4), indicating that their deficit in novel word production was not just an artefact of the scoring procedure used to derive the expressive score. This finding also means that the inconsistent children’s poor performance in pronouncing novel words cannot be solely attributed to a difficulty in word retrieval, i.e. recalling the names of the pigs.

2. Another explanation for the inconsistent group’s poorer performance may be that their errors resulted from incomplete output lexical representations (Dinnsen, Elbert & Weismer, 1981; Spencer, 1986). For example, sandal might be represented as /fricative + aendal/ allowing variable surface realisations such as [faendal or Jaendal]. Children fill gaps in their output lexicon by making hypotheses on the basis of their phonotactic knowledge of the language (Iverson & Wheeler, 1987). Previous research has shown that children who make inconsistent errors have adequate knowledge of what is phonologically legal (Dodd et al., 1989) and would therefore be able to fill in the spaces in an incomplete output lexical representation appropriately. Also, the type of variation typical of children who make inconsistent errors is much greater than that predicted by gaps in a word’s lexical representation. The following examples of variable productions are from children classified as inconsistent: [khku] and [h elik~ka] for helicopter; [raku] and [bae:um] for vacuum cleaner; [fw~s] and [sIJ] for fish; [enzent] and [elabqk] for elephant, and [ a ~ d ~ j ~ ] and [akl~nt] for elephant. Such widely differing pronunciations of the same words cannot be explained by the hypothesis that variable errors arise from incomplete representations in an output lexicon because they differ not simply in terms of phonemes in particular con- texts but also in the number and structure of syllables.

3. Children making inconsistent errors may have an impaired ability to establish motor plans from fully specified internal phonological representations of words. This hypothesis is supported by the poorer performance of the inconsistent subjects on the motor accuracy task as compared with the other subject groups. The inconsistent group had difficulty planning or organising the components of this task. They were able to use appropriate


pencil grips but were unable to plan and coordinate action to perform as well as the other groups. The phonological production task has several component processes, similar to the timed tracing task. The inconsistent group had intact peripheral motor control (none of the subjects had any peripheral motor difficulties). They were also usually able to articulate iso- lated phonemes (as indicated by their original diagnosis of phonological disorder as opposed to dysarthria or articulation disorder). Thus their deficit would seem to be an impaired ability to formulate a plan for timing and sequencing phonetic segments. Children who make inconsistent errors may, in fact, trial a new motor plan for a word each time it is produced, resulting in the observed inconsistency of surface errors. One contributing factor to this inconsistency may be an impaired ability to establish complete internal mental representations for new words, given the group’s trend towards poorer performance on the novel word receptive learning task.

In contrast, the finding that the phonologically delayed and deviant consistent groups did not differ from the control group on any of the motor planning tasks assessed suggests that their deficit is not in establishing motor plans for speech production. The delayed group, whose rate of phonological acquisition is slow and whose errors are typical of normal development, may not have any deficit. Rather their speech errors may be attributable to an impoverished language learning environment or slow neurological maturation (Dodd, 1993). Previous research suggests that children who make deviant consistent errors have a cognitive/linguistic deficit. They perform poorly on tasks involving the detection of phonological legality (Dodd et al., 1989), rhyme recognition (Brierly, 1987), phoneme segmentation skills (Bird & Bishop, 1992), and have difficulties in the acquisition of literacy skills (Dodd & Cockerill, 1986; Dodd, Russell & Oerlemans, 1994). All these tasks tap knowledge of the phonological system, and their deficit would seem to point to a cognitive deficit in rule abstraction at the lexical-phonological level of production (Dodd et al., 1989). The poor performance of the inconsistent group on the motor planning and novel word learning tasks suggests that the deficit underlying inconsistent errors is different from deficits underlying phonological delay or consistent use of non-developmental processes.

These findings have implications for models of child phonology, because they demand that both linguistic and motor planning skills be included to describe accurately the range of mental processes mediating speech production. The findings also have clinical implications. Assessment of disordered speech needs to include not only description of surface error patterns, but also tests that enable diagnosis of the deficit(s) underlying a child’s speech disorder. Cost-effective treatment necessitates the use of specific intervention approaches that target specific deficits.

ACKOWLEDGEMENTS Our thanks to the speech pathologists who referred children to the study, and parents and children for their cooperation and patience. The study was funded by an Australian Research Council grant.


APPENDIX I Examples of Developmental and Deviant Phonological Processes

Developmental processes

Final consonant deletion Cluster reduction Weak syllable deletion Reduplication Revocalic voicing Final consonant devoicing Fronting of fricatives and velars Stopping of fricatives and affricates Gliding Deaffrication Assimilation

Deviant processes

Initial consonant deletion of a class of phonemes Medial consonant deletion Intrusive consonants Backing Medial consonant substitutions Denasalisation Devoicing of a class of phonemes Sound preference substitutions Use of non-native language phonemes

APPENDIX II

Criteria for Group Assignment Delayed Group All phonological processes were developmental. Use of at least two processes that were not age-appropriate.

Deviant consistent group Use of at least two deviant phonological processes applied consistently so that errors were predictable.

Inconsistent group Use of deviant errors with no observable error pattern, and no noted articulatory groping on volitional phoneme production.

APPENDIX 111 Examples of Repeated Pronunciations of the Same 25 Words ILom Children in Subgroups of Phonological Disorder

Target Control

dinosaur d a I m s 3 daImM3 daImAs3

4;11

slippery slide slrpri drp slzpri drp shpri dIp

shark Sak Sak Sak

Bert b3t b3t b3t

Delayed 4;lO

darntw dar nM3 daxnAs3

Jrpwi saxd srpwi sard JIpwi JaId

sak sak sak

b3t* b3t b3t

Consistent 4;9

daInAg3 damw daInAg3

gwIpi dIp gwrpi dIp gwrpi dIp

gak

gak ga

b3t* b3t* b3t*

Inconsistent 4;O

daIxs3wi d a I X 3 daI:Amwi

w ~ p waI fWI pwai fwI fwaI

Sak Sak Sak

b3t* b3t* b3t*

Inconsistent 4;7

d a I M S 3 d a m w d a I M S 3

srpi drp sIpi sarn sipi saI

Sak Sak sak

b3t* b d * bDt*


Target Control Delayed 4;11 4;lO

eaqkju saqkju Oaqkju saqkju

jump d3AmP djAmp d3AmP djamp d3AmP djAmp

thank you freqkju Bagkju*

birthday cake b30de1 kerk bs fde~ teik

fish

elephant

witch

tongue

chips

girl

vacuum cleaner

rain

parrot

bridge

kangaroo

Inconsktent 4;O

daqku deqku dqku*

dAmp dAmp dAP

b3dei b s e d e ~ keIk bs fde~ teIk bsdei kerk bseder bsedei keIk bsfder teIk bsder keik bseder

frl f1s 6' 21

f r l f1s S' SI f r l V I S S' d31l

dAfant aelafant Elan 13 ehfant aelafant elan E:3

Elhfant aelafant Elan E

wits wrts W I wit W I t S wits W I w1t wItr wrts W I W I t

w w w s d 4 w! w w dALl WI m w g dALl

tJ1ps tlrps !VPi d y p i trips thp1z SIPi d p p i tlrps tSlPIZ 91Pi d31pi

gsl d3 g3 63 gsl d3 g3 g3 S3l d3 s3 giu

vzkjum klina bakjum tfina bzkjum MA gAp k l i n ~ vzkjum Mhia vakjum tlina bzkjum kwhA gAp k l i n ~ vzkjum klina vzkjum tlina baekjum kwinrl bak klinrl

rem w e m q r e m q wemi rerniq weIniq r e m q weinxq reInIq weInIq rexniq wexnIq

pzrat pawat prerat bawa* prerat pawat parat bawa* parat pawat parat bawa*

br1d3 bw Idz br I fWlt

br1d3 bwIdz br I fWIt

kzqgAru taeqgawu ki-eqm gEwu kzqghru . tieqgawu kaeyru gzeqawu

bridj bwrdz brr hwIt 1 fId

kreqgm mqgawu kreqAru gEqAWU

Inconsistent 4;7

daqkju daqkju daeqkju

d3AmP d3AmP t h m

b3 edei keI k bssei keik bs fde~ keIk

fIl f i l W I I

anrlnt AnAnant AnAnant

wits wits WItJ

weman weIn weman

pajat* paijad pajad

br1d3 r1d3 bud3


Target

helicopter

ladybird

five

umbrella

teeth

scissors

zebra

*Imitated.

Control 4;ll

helakDptA he1akDpth helakDpth

lerdi bidal leIdi bidal leIdi bidal

fa1 v faxv faIv

AmbrEh

hmbrelh hmbrelh

ti 8 tie tie

S I W Z S I W Z S I W Z

E b r h E b r h E b r h

Delayed 4;lO

helitopth helitopth helitDptA

jeIdi bitu jeidi bitu jeidi bitu

farv faIv faxv

hnbWElA* AnbwElA hlhbweh

tif tif tif

S I W Z S I W Z S I Z a Z

izbwh z b w h ZbwA

Consistent 4;9

hdkDptA

hhlkopth

reli bidal exdi b3d e id i bidal

gar gal gaxd

A n k h r \ m k L A m k L

ti ti ti

g I daz gxdaz gidaz

gmrA g w r \ grerrl

hDlkDph

Inconsistent 4;O

hegoth hegoth h&gDtA

leidi brzg lexdi bhg leIdi bitu

fwaiv* fwaIv* faib

hnfwe fwedu hrnfede

di di di

S 1 Sth S I S t h S I S t h

S&SA

S&VWA* sebh

Inconsistent 4;7

h&VatDtA he1 tei ph heddatDpA

lexdi bDd* leidi bilu leidi bilu

fare fa10 fax0

hdhbwedh i m k h hmb&

t i S t i e t i e

s I dad sizad s i d d

d3ebh d3ebh d 3 e b ~

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the motor planning abilities of phonologically disordered children

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