Lingual articulation in children with developmental speech disorders

This thesis presents thirteen research papers published between 1987-97, and a summary and discussion of their contribution to the field of developmental speech disorders. The publications collectively constitute a body of work with two overarching themes. The first is methodological: all the publications report articulatory data relating to tongue movements recorded using the instrumental technique of electropalatography (EPG). The second is the clinical orientation of the research: the EPG data are interpreted throughout for the purpose of informing the theory and practice of speech pathology. The majority of the publications are original, experimental studies of lingual articulation in children with developmental speech disorders. At the same time the publications cover a broad range of theoretical and clinical issues relating to lingual articulation including: articulation in normal speakers, the clinical applications of EPG, data analysis procedures, articulation in second language learners, and the effect of oral surgery on articulation. The contribution of the publications to the field of developmental speech disorders of unknown origin, also known as phonological impairment or functional articulation disorder, is summarised and discussed. In total, EPG data from fourteen children are reported. The collective results from the publications do not support the cognitive/linguistic explanation of developmental speech disorders. Instead, the EPG findings are marshalled to build the case that specific deficits in speech motor control can account for many of the diverse speech error characteristics identified by perceptual analysis in previous studies. Some of the children studied had speech motor deficits that were relatively discrete, involving, for example, an apparently isolated difficulty with tongue tiplblade groove formation for sibilant targets. Articulatory difficulties of the 'discrete' or specific type are consistent with traditional views of functional lingual articulation in developmental speech disorders articulation disorder. EPG studies of tongue control in normal adults provided insights into a different type of speech motor control deficit observed in the speech of many of the children studied. Unlike the children with discrete articulatory difficulties, others produced abnormal EPG patterns for a wide range of lingual targets. These abnormal gestures were characterised by broad, undifferentiated tongue-palate contact, accompanied by variable approach and release phases. These 'widespread', undifferentiated gestures are interpreted as constituting a previously undescribed form of speech motor deficit, resulting from a difficulty in controlling the tongue tip/blade system independently of the tongue body. Undifferentiated gestures were found to result in variable percepts depending on the target and the timing of the particular gesture, and may manifest as perceptually acceptable productions, phonological substitutions or phonetic distortions. It is suggested that discrete and widespread speech motor deficits reflect different stages along a developmental or severity continuum, rather than distinct subgroups with different underlying deficits. The children studied all manifested speech motor control deficits of varying degrees along this continuum. It is argued that it is the unique anatomical properties of the tongue, combined with the high level of spatial and temporal accuracy required for tongue tiplblade and tongue body co-ordination, that put lingual control specifically at risk in young children. The EPG findings question the validity of assumptions made about the presence/absence of speech motor control deficits, when such assumptions are based entirely on non-instrumental assessment procedures. A novel account of the sequence of acquisition of alveolar stop articulation in children with normal speech development is proposed, based on the EPG data from the children with developmental speech disorders. It is suggested that broad, undifferentiated gestures may occur in young normal children, and that adult-like lingual control develops gradually through the processes of differentiation and integration. Finally, the EPG fmdings are discussed in relation to two recent theoretical frameworks, that of psycho linguistic models and a dynamic systems approach to speech acquisition

Abnormal patterns of tongue-palate contact in the speech of individuals with cleft palate

Individuals with cleft palate, even those with adequate velopharyngeal function, are at high risk for disordered lingual articulation. This article attempts to summarize current knowledge of abnormal tongue-palate contact patterns derived from electropalatographic (EPG) data in speakers with cleft palate. These data, which have been reported in 23 articles published over the past 20 years, have added significantly to our knowledge about cleft palate speech. Eight abnormal patterns of tongue-palate contact are described and illustrated with data from children and adults with repaired cleft palate. The paper also discusses some of the problems in interpreting EPG data from speakers with abnormal craniofacial anatomy and emphasizes the importance of quantifying relevant aspects of tongue-palate contact data. Areas of research requiring further investigation are outlined

Using EPG data to display articulatory separation for phoneme contrasts

A recurring difficulty for researchers using electropalatography (EPG) is the wide variation in spatial patterns that occurs between speakers. High inter speaker variability, combined with small numbers of participants, makes it problematic (i) to identify differences in tongue palate contact across groups of speakers and (ii) to define “normal” patterns during visual feedback therapy. This paper shows how graphing EPG data in terms of articulatory separation of phoneme contrasts reduces these two problems to some extent. The graphs emphasise the importance of establishing the presence and extent of separation, as revealed in the EPG data, for phoneme contrasts produced by speakers. Separation graphs for contrasts /i/ - /u/, /s/ - /ʃ/ and /t/ - /k/ are presented using EPG data from adults and children with typical speech and those with speech disorders. When used in conjunction with acoustic and auditory perceptual analyses, it is proposed that representing articulation data in terms of separation will prove useful for a range of clinical and research purposes

Articulatory characteristics of the occlusion phase of /tS/ compared to /t/ in adult speech.

This study used electropalatography (EPG) to investigate articulatory characteristics of /tS/ and /t/ occlusion in order to provide normative data to be used for the diagnosis and treatment of individuals with speech disorders. EPG data from the EUR-ACCOR database were analysed for nonsense VCV sequences containing /tS/ and /t/ in nine vowel contexts for seven English speaking adults. The main results of this study are that all speakers had a significantly more posterior placement for /tS/ compared to /t/ and that placement was stable during the occlusion phase of both /tS/ and /t/. For most speakers, the occlusion phase was longer for /tS/ compared to /t/, the occlusion phase generally involved more EPG contact and was slightly more variable in /tS/ compared to /t/, but these differences were not statistically significant for all speakers. The implications of the results for diagnosing and treating speech disorders are discussed

Undifferentiated lingual gestures and their implications for speech disorders in children

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Visual feedback therapy with electropalatography

Electropalatography (EPG) is an instrumental technique that detects the tongue’s contact against the hard palate during speech and creates a visual display of the resulting patterns. This chapter focuses on EPG as a visual feedback device in therapy for children with speech sound disorders. Tongue-palate contact information is rich in detail and as a result it can be used for diverse research and clinical purposes. Examples of clinically relevant information contained in EPG data are place of articulation, lateral bracing, groove formation, timing of tongue movements and coarticulation. Furthermore, the technique records measurable amounts of contact for sound targets that are frequently produced as errors by children with speech sound disorders (e.g., /δ/, /Ʃ/, /τƩ/). These features make EPG valuable for both diagnosis and therapy. During EPG therapy, children’s abnormal articulation patterns are revealed to them on the computer screen and they can use this dynamic visual feedback display to help them produce normal contact patterns. An attractive property of EPG as a therapy device is that the visual display is relatively intuitive. This means that children can understand the link between the speech sounds they hear and the associated contact patterns displayed on the screen. There is now an extensive literature on the benefits of using EPG in therapy, but the quality of evidence would improve by conducting large clinical trials in the future

Speech errors and articulatory gestures: an electropalatographic investigation

Jedan od glavnih zaključaka tradicionalnih istraživanja govornih pogrešaka, koja se temelje na slušnom zamjećivanju pogrešaka u govoru i njihovu transkribiranju, je da je glasnik najmanja jedinica govora zahvaćena pogreškom. Ipak, istraživači takva pristupa nisu u potpunosti odbacili mogućnost da na neke pogreške, npr. zamjene jednog fonema drugim, ne utječu i jedinice manje od segmenta, npr. razlikovna obilježja. Suvremene studije, koje govorne pogreške analiziraju s pomoću nekih od instrumentalnih metoda za istraživanje govora, npr. elektropalatografijom, pokazuju da se govorne pogreške mogu dogoditi i na razini nižoj od jednog glasnika – tj. mogu zahvatiti artikulacijsku gestu. Takve se pogreške manifestiraju kao istodobna produkcija gesti dvaju glasnika – ciljanoga i uljeza. S obzirom da takve pogreške predstavljaju stupnjeviti pomak od jednog segmenta ka drugomu, za razliku od kategorijalnih pogrešaka, nazivaju se gradacijskim pogreškama. Cilj je ovoga rada provjeriti pojavu gradacijskih pogrešaka u izgovoru, koristeći elektropalatografsku metodu. Analiza je obuhvatila dva ciljana suglasnika – /l/ i /r/, koje je izgovorilo deset izvornih govornica hrvatskoga jezika, ponavljajući brzalicu Kralj Karlo i kraljica Klara krali klarinet uobičajenim tempom. Svaka je pojavnica ciljanih suglasnika svrstana u jednu od četiriju kategorija: (1) perceptivno i artikulacijski i ispravan izgovor (P1A1); (2) artikulacijski ispravan, ali perceptivno neispravan izgovor (P0A1); (3) perceptivno ispravan, ali artikulacijski neispravan izgovor (P1A0) i (4) perceptivno i artikulacijski neispravan izgovor (P0A0). Artikulacijska ispravnost određena je tipičnim elektropalatogramom ciljanoga glasnika, a perceptivna ispravnost time zvuči li ciljani glasnik kao tipično ostvarenje toga glasnika u hrvatskome jeziku. Analiza je pokazala prisutnost i gradacijskih i kategorijalnih pogrešaka. Time je ovo istraživanje potvrdilo rezultate nekih drugih instrumentalnih istraživanja, koje pokazuju kako tradicionalna metoda koja se temelji isključivo na slušanju i zapisivanju pogrešaka nije dovoljna da zamijeti sva odstupanja od govornoga plana. Ono također ukazuje na potrebu revidiranja postojećih modela fonološkog kodiranja u proizvodnji govora, uzimajući u obzir gradacijske pogreške.One of the major findings of traditional investigations of speech errors is that a single segment is the smallest unit affected by speech errors, although the possibility that units smaller than the segment could play a role in explaining speech errors was not entirely rejected. A number of relatively recent studies using instrumental kinematic techniques for speech analysis bring evidence that errors often occur at subsegmental units of speech production, i.e. at the level of articulatory gestures. Such errors occur due to the coproduction of articulatory gestures, whereby the gestures from both the target consonant and the competing speech sound overlap. As they represent the gradient shift from one segment to another, they are often called gradient errors. Such processes are almost impossible to capture without the use of instrumental kinematic techniques, such as electropalatography (EPG). Th ere are no instrumental kinematic studies of speech errors in Croatian speech. Th us, the aim of this paper is to use EPG to investigate speech errors produced in one Croatian tongue twister. The analysis was focused on /r/ and /l/ targets produced by 10 native female speakers of Croatian, while producing the tongue twister which facilitated speech errors in these two sounds. Each token of the target consonant was classifi ed in one of the four categories: (1) perceptually and articulatorily correct production (P1A1); (2) articulatorily correct but perceptually incorrect production (P0A1); (3) perceptually correct but articulatorily incorrect production (P1A0) and (4) perceptually and articulatorily incorrect production (P0A0). Th e classifi cation was made by the authors via auditory analysis and visual inspection of spectrograms and electropalatograms prior to the quantitative kinematic analysis. Subsequent analyses showed evidence of gradient errors, which would not be detected without the use of instrumental kinematic techniques. Th is investigation supports the claim that traditional method of collecting speech errors by perceptual analysis only is not sensitive enough to detect the subtleties of erroneous productions and speech motor control

Place of articulation of anterior nasal versus oral stops in Croatian

The purpose of this investigation is to analyse the place of articulation of anterior nasal versus oral stops in Croatian. Although there is agreement that placement for /n/ and /t d/ is in the anterior region, there is disagreement among different authors about the precise place of articulation for these sounds. Some authors view these targets as sharing identical placement while others view placement of /n/ as more posterior to /t d/. In this paper we use electropalatography (EPG) to investigate whether placement for these sounds is the same or different. The speech of six participants was recorded for the purposes of this study. The speech material consisted of 972 VCV sequences (V = /i a u/, C = /n t d/). Four EPG indices were analysed: the ACoG measure, the amount of contact at dental and alveolar articulatory zones (dentoalveolar articulation being inferred indirectly), incomplete EPG closures and the lateral contact measure. Coarticulatory effects of vowels on placement were also measured. The results showed that /n t d/ generally shared the place of articulation in the dentoalveolar region, but also that relating quantitative physiological data to specific places of articulation should be done cautiously, taking into account variability in individual productions. The analyses also showed that /n/ had more incomplete EPG closures and a significantly lower amount of lateral contact when compared with /t/ and /d/. The nasal was more variable and showed less coarticulatory resistance in different vowel contexts than /t/ and /d/. The results of this study are discussed in terms of existing descriptions of Croatian consonant system and in light of cross-linguistic findings

Differences in EPG contact dynamics between voiced and voiceless lingual fricatives

Achieving voicing during fricatives is complex because voicing and frication require opposite production strategies that must be managed effectively at the supralaryngeal level. Previous research has suggested that there are differences in tongue-to-palate contact patterns that are conditioned by voicing. However, findings have been restricted to a single time point and have been generally inconclusive. This study used electropalatography (EPG) to investigate differences in the dynamics of contact in voiced and voiceless lingual fricatives. Participants were six typically speaking Croatian adults. The speech material consisted of symmetrical VCV sequences, where C was /s z ʃ ʒ/. EPG measures were taken throughout the fricatives and indices were used to quantify place of articulation (CoG), groove width and target configuration onset. The EPG measures showed similar results for voiced and voiceless fricatives during their central portions. However, there were notable differences at the periphery of the fricative period, the most significant being that the voiceless fricatives reached a stable period in terms of tongue placement and groove configuration later than the voiced fricatives. The results support aerodynamic evidence that voiced and voiceless fricatives differ in the onset and the offset of turbulence