The development of reading competency is one of the most significant pedagogical achievements during the first few years of schooling. Although most children learn to read successfully when exposed to reading instruction, up to 18% of children experience significant reading difficulty (Shaywitz, 1998). As a group, young children with speech impairment are at risk of reading impairment, with approximately 50% of these children demonstrating poor acquisition of early reading skills (Nathan, Stackhouse, Goulandris, & Snowling, 2004; Larivee & Catts, 1999). A number of variables contribute to reading outcomes for children with speech impairment including co-occurring language impairment, the nature and severity of their speech impairment as well as social and cultural influences. An area of research that has received increasing attention is understanding how access to the underlying sound structure or phonological representations of spoken words stored in long-term memory account for reading difficulties observed in children (Elbro, 1996; Fowler, 1991). Researchers have hypothesised that children with speech impairment may be at increased risk of reading disability due to deficits at the level of phonological representations (Bird, Bishop, & Freeman, 1995). Phonological representation deficits can manifest in poor performance on tasks that require children to think about the sound structure of words. Knowledge about the phonological components of words is commonly referred to as phonological awareness. Identifying and manipulating phonemes within words are examples of phonological awareness skills. Some children with speech impairment perform poorly on phonological awareness measures compared to children without speech difficulties (Bird et al., 1995; Carroll & Snowling, 2004; Rvachew, Ohberg, Grawburg, & Heyding, 2003). As performance on phonological awareness tasks is a strong predictor of early reading ability (Hogan, Catts, & Little, 2005), there is an important need to determine if children with speech impairment who demonstrate poor phonological awareness, have deficits at the level of phonological representations. This thesis reports a series of studies that investigated the relationship between phonological representations, phonological awareness, and word decoding ability in children with moderate to severe speech impairment. A child with complex communication needs (CCN) who used Augmentative and Alternative Communication (AAC) was also examined to determine how the absence of effective articulation skills influences the development of phonological representations. The study employed a longitudinal design to compare the performance of nine children (aged 3:09-5:03 at initial assessment) with moderate to severe speech impairment and 17 children with typical speech development on novel assessment measures designed to determine characteristics of children's phonological representations. The tasks required children to judge the accuracy of spoken multisyllable words and newly learned nonwords. The relationships between performance on these tasks and measures of speech, phonological awareness and early print decoding were also examined. Four assessment trials were implemented at six-monthly intervals over an 18-month period. The first assessment trial was administered approximately 6 to12 months before children commenced school. The fourth trial was administered after children had completed 6 to 12 months of formal education. The child with CCN completed three assessment trials over a period of 16 months. Data analyses revealed that the children with speech impairment had significantly greater difficulty (p<0.01) judging mispronounced multisyllable words compared to their peers with typical speech development. As a group, children with speech impairment also demonstrated inferior performance on the judgment of mispronounced forms of newly learned nonwords (p<0.05). No group differences were observed on the judgment of correctly pronounced real and nonword stimuli. Significant group differences on speech production and phoneme segmentation tasks were identified at each assessment trial. Moderate to high correlations (i.e., r = 0.40 to 0.70) were also observed between performance on the phonological representation tasks and performance on phonological awareness and speech production measures at each trial across the study. Although no significant group differences were observed on the nonword decoding task, 4 of the 9 children with speech impairment could not decode any letters in nonwords (compared to only 1 child without speech impairment) at the final assessment trial when children were 6-years-old. Two children with speech impairment showed superior nonword decoding ability at trial 3 and 4. The within-group variability observed on the nonword decoding task highlighted the heterogeneity of children with speech impairment. The performances of four children with speech impairment with differing types of speech error patterns were analysed to investigate the role of phonological representations in their speech and phonological awareness development. The child with delayed speech development and excellent phonological awareness at trial 1, demonstrated superior phonological awareness and word decoding skills at age 6 years, although his performance on phonological representation tasks was inconsistent across trials. In contrast, a child with delayed development and poor early phonological awareness demonstrated weak performance on phonological representation, phonological awareness, and decoding at each successive assessment trial. The child with a high percentage of inconsistent speech error patterns generally demonstrated poor performance on phonological representation, phonological awareness and decoding measures at each of the 4 assessment trials. The child with consistent and unusual speech error patterns showed increasingly stronger performance on the phonological representation tasks and average performance on phonological awareness but limited word decoding ability at age 6. The 11-year-old girl with CCN, whose speech attempts were limited and unintelligible, demonstrated below average performance on phonological representation tasks, suggesting that an absence of articulatory feedback may negatively influence the development of well-specified phonological representations. This thesis provides evidence for the use of receptive tasks to identify differences in the phonological representations of children with and without speech impairment. The findings also provide support for the link between the representation of phonological information in long-term memory and children's speech production accuracy, phonological awareness and print decoding ability. The variable performance of some children with speech impairment and the child with cerebral palsy demonstrate the need to consider individual characteristics to develop an understanding of how children store and access speech sound information to assist their acquisition of early reading skills.

Children with childhood apraxia of speech (CAS) are likely to experience severe and persistent spoken and written language disorder. There is a scarcity of intervention research, however, investigating techniques to improve the speech and literacy outcomes of this population. The series of 5 experiments reported in this thesis investigated phonological awareness and early reading development in children with CAS and trialled a new intervention designed to advance the spoken and written language development of those affected. In the first experiment (presented in Chapter 2), a comparison of 12 children with CAS, 12 children with inconsistent speech disorder (ISD), and 12 children with typical speech-language development (TD) revealed that children with CAS may be particularly susceptible to phonological awareness and reading deficits. There was no difference in the articulatory consistency and speech severity of the CAS and ISD groups, and no difference in the receptive vocabulary of the CAS, ISD, and TD groups. The children with CAS exhibited poorer phonological awareness scores than the comparison groups and had a greater percentage of participants performing below the expected range for their age on letter knowledge, real word decoding, and phonological awareness normative measures. The children with CAS and ISD performed inferiorly than the children with TD on a receptive phonological representation task. The results showed that the children with CAS had a representational component to their disorder that needed to be addressed in intervention. In the second experiment (presented in Chapter 3), a follow-up pilot study was conducted to examine the long-term effects of a previously conducted intensive integrated phonological awareness programme (7 hours of intervention over 3 weeks) on 2 children with CAS. The children aged 7;3 and 8;3 at follow-up assessment had previously responded positively to the intervention. Results showed that the children were able to maintain their high accuracy in targeted speech repeated measures over the follow-up period. One child was also able to maintain her high accuracy in phonological awareness repeated measures. The children performed superiorly on a standardised phonological awareness measure at follow-up than at pre-intervention. Non-word reading ability showed a sharp increase during the intervention period, while minimal gains were made in this measure over the follow-up period. The findings suggested that an integrated intervention was a potential therapeutic approach for children with CAS. In the third experiment (presented in Chapter 4), the effectiveness of an integrated phonological awareness programme was evaluated for the 12 children (identified in the first experiment) aged 4 to 7 years with CAS. A controlled multiple single-subject design with repeated measures was employed to analyse change in trained and untrained speech and phoneme segmentation targets. A comparative group design was used to evaluate the phonological awareness, reading, and spelling development of the children with CAS compared to their peers with TD over the intervention. The children participated in two 6- week intervention blocks (2-sessions per week) separated by a 6-week withdrawal block. Seven children with CAS made significant gains in their production of trained and untrained speech words with 7 of these children demonstrating transfer of skills to connected speech for at least one target. Ten children showed significant gains in phoneme awareness, and 8 of these children demonstrated transfer of skills to novel phoneme awareness tasks. As a group, the children with CAS demonstrated accelerated development over the intervention period in letter knowledge, phonological awareness, word decoding, and spelling ability compared to their peers with typical development. In the fourth experiment (presented in Chapter 5), the speech, phonological awareness, reading, and spelling skills of children with CAS and TD were re-evaluated 6- months following completion of the intervention programme. A measure of reading accuracy and reading comprehension in a text reading task was administered to the children with CAS. There was no difference in the performance of the children with CAS in post-intervention and follow-up assessments. The children with CAS and children with TD presented with similar relative change in phonological awareness, reading, and decoding measures over the follow-up period. The connected reading performance of children with CAS mirrored their phonological awareness and decoding skills. The findings demonstrated that children with CAS were able to maintain gains achieved during the intervention but may need further support to promote sustained development in written language. In the fifth experiment (presented in Chapter 6), the long-term effects of the integrated phonological awareness programme for identical twin boys who participated in the research intervention at pre-school were examined. The study examined Theo and Jamie's spoken language, phonological awareness, reading, and spelling development during their first year of schooling. The results pointed to the benefit of providing phonological awareness within a preventative framework for children with CAS. Theo and Jamie experienced continued growth in speech and phonological awareness skills. They exhibited age-appropriate reading and spelling development during their first year of formal literacy instruction. It was concluded from this series of experiments that children with CAS are particularly vulnerable to phonological awareness and early reading difficulty, and that an integrated phonological awareness intervention is an effective means of developing speech, phonological awareness, reading, and spelling skills in most children with CAS. The intervention appears to target processes underlying spoken and written language development in this population. The results are discussed within a phonological representation deficit hypothesis of CAS and clinical implications of the findings are highlighted.

We used fMRI to examine the neural substrates of sublexical phoneme-grapheme conversion during spelling in a group of healthy young adults. Participants performed a writing-to-dictation task involving irregular words (e.g., choir), plausible nonwords (e.g., kroid), and a control task of drawing familiar geometric shapes (e.g., squares). Written production of both irregular words and nonwords engaged a left hemisphere perisylvian network associated with reading/spelling and phonological processing skills. Effects of lexicality, manifested by increased activation during nonword relative to irregular word spelling, were noted in anterior perisylvian regions (posterior inferior frontal gyrus/operculum/precentral gyrus/insula), and in left ventral occipito-temporal cortex. In addition to enhanced neural responses within domain-specific components of the language network, the increased cognitive demands associated with spelling nonwords engaged domain-general frontoparietal cortical networks involved in selective attention and executive control. These results elucidate the neural substrates of sublexical processing during written language production and complement lesion-deficit correlation studies of phonological agraphia.

A phonological disorder is a communication disorder of the speech sound system characterized by an impaired ability to use developmentally expected speech sounds and sound patterns to communicate with others (Bauman-Waengler, 2004). This impairment affects the clarity of a child's speech and how easily a child's speech can be understood. As stated in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 1994), difficulties with speech sound production may interfere with academic achievement, social communication, or future occupational achievement. Children with phonological impairments are generally viewed as being at risk for reading difficulties (American Speech-Language-Hearing Association, 2001).Clinicians and researchers in speech-language pathology agree that efficient treatment of children who have moderate to severe phonological disorders is critical. Although imitation and structured practice are primary strategies employed by speech- language pathologists for practicing speech production, using communicative tasks to facilitate generalization during phonological intervention has been suggested in the literature.The purpose of this study was to determine if communication-centered phonological intervention would be effective in improving speech production in preschool children with moderate to severe phonological disorders. A single subject multiple probe across subjects research design (Horner andamp; Baer, 1978) was used to assess the effectiveness of communication-centered phonological intervention with three preschool children. The communication-centered phonological intervention in this investigation consisted of the combined application of focused stimulation of key words during joint storybook reading and interactive practice of key words using communicative feedback.All three subjects demonstrated some type of phonological improvement following the communication-centered intervention. Two out of the three subjects demonstrated improvement in the use of the target phonological patterns during theintervention sessions with one of these participants demonstrating generalization of the target phonological pattern to conversational speech. Although the third subject did not demonstrate improvement during the intervention period, follow-up testing revealed some system-wide changes in his phonology that may be attributed to the intervention. Further investigation of communication-centered phonological intervention is warranted.

The development of reading competency is one of the most significant pedagogical achievements during the first few years of schooling. Although most children learn to read successfully when exposed to reading instruction, up to 18% of children experience significant reading difficulty (Shaywitz, 1998). As a group, young children with speech impairment are at risk of reading impairment, with approximately 50% of these children demonstrating poor acquisition of early reading skills (Nathan, Stackhouse, Goulandris, & Snowling, 2004; Larivee & Catts, 1999). A number of variables contribute to reading outcomes for children with speech impairment including co-occurring language impairment, the nature and severity of their speech impairment as well as social and cultural influences. An area of research that has received increasing attention is understanding how access to the underlying sound structure or phonological representations of spoken words stored in long-term memory account for reading difficulties observed in children (Elbro, 1996; Fowler, 1991). Researchers have hypothesised that children with speech impairment may be at increased risk of reading disability due to deficits at the level of phonological representations (Bird, Bishop, & Freeman, 1995). Phonological representation deficits can manifest in poor performance on tasks that require children to think about the sound structure of words. Knowledge about the phonological components of words is commonly referred to as phonological awareness. Identifying and manipulating phonemes within words are examples of phonological awareness skills. Some children with speech impairment perform poorly on phonological awareness measures compared to children without speech difficulties (Bird et al., 1995; Carroll & Snowling, 2004; Rvachew, Ohberg, Grawburg, & Heyding, 2003). As performance on phonological awareness tasks is a strong predictor of early reading ability (Hogan, Catts, & Little, 2005), there is an important need to determine if children with speech impairment who demonstrate poor phonological awareness, have deficits at the level of phonological representations. This thesis reports a series of studies that investigated the relationship between phonological representations, phonological awareness, and word decoding ability in children with moderate to severe speech impairment. A child with complex communication needs (CCN) who used Augmentative and Alternative Communication (AAC) was also examined to determine how the absence of effective articulation skills influences the development of phonological representations. The study employed a longitudinal design to compare the performance of nine children (aged 3:09-5:03 at initial assessment) with moderate to severe speech impairment and 17 children with typical speech development on novel assessment measures designed to determine characteristics of children's phonological representations. The tasks required children to judge the accuracy of spoken multisyllable words and newly learned nonwords. The relationships between performance on these tasks and measures of speech, phonological awareness and early print decoding were also examined. Four assessment trials were implemented at six-monthly intervals over an 18-month period. The first assessment trial was administered approximately 6 to12 months before children commenced school. The fourth trial was administered after children had completed 6 to 12 months of formal education. The child with CCN completed three assessment trials over a period of 16 months. Data analyses revealed that the children with speech impairment had significantly greater difficulty (p<0.01) judging mispronounced multisyllable words compared to their peers with typical speech development. As a group, children with speech impairment also demonstrated inferior performance on the judgment of mispronounced forms of newly learned nonwords (p<0.05). No group differences were observed on the judgment of correctly pronounced real and nonword stimuli. Significant group differences on speech production and phoneme segmentation tasks were identified at each assessment trial. Moderate to high correlations (i.e., r = 0.40 to 0.70) were also observed between performance on the phonological representation tasks and performance on phonological awareness and speech production measures at each trial across the study. Although no significant group differences were observed on the nonword decoding task, 4 of the 9 children with speech impairment could not decode any letters in nonwords (compared to only 1 child without speech impairment) at the final assessment trial when children were 6-years-old. Two children with speech impairment showed superior nonword decoding ability at trial 3 and 4. The within-group variability observed on the nonword decoding task highlighted the heterogeneity of children with speech impairment. The performances of four children with speech impairment with differing types of speech error patterns were analysed to investigate the role of phonological representations in their speech and phonological awareness development. The child with delayed speech development and excellent phonological awareness at trial 1, demonstrated superior phonological awareness and word decoding skills at age 6 years, although his performance on phonological representation tasks was inconsistent across trials. In contrast, a child with delayed development and poor early phonological awareness demonstrated weak performance on phonological representation, phonological awareness, and decoding at each successive assessment trial. The child with a high percentage of inconsistent speech error patterns generally demonstrated poor performance on phonological representation, phonological awareness and decoding measures at each of the 4 assessment trials. The child with consistent and unusual speech error patterns showed increasingly stronger performance on the phonological representation tasks and average performance on phonological awareness but limited word decoding ability at age 6. The 11-year-old girl with CCN, whose speech attempts were limited and unintelligible, demonstrated below average performance on phonological representation tasks, suggesting that an absence of articulatory feedback may negatively influence the development of well-specified phonological representations. This thesis provides evidence for the use of receptive tasks to identify differences in the phonological representations of children with and without speech impairment. The findings also provide support for the link between the representation of phonological information in long-term memory and children's speech production accuracy, phonological awareness and print decoding ability. The variable performance of some children with speech impairment and the child with cerebral palsy demonstrate the need to consider individual characteristics to develop an understanding of how children store and access speech sound information to assist their acquisition of early reading skills.

Children with childhood apraxia of speech (CAS) are likely to experience severe and persistent spoken and written language disorder. There is a scarcity of intervention research, however, investigating techniques to improve the speech and literacy outcomes of this population. The series of 5 experiments reported in this thesis investigated phonological awareness and early reading development in children with CAS and trialled a new intervention designed to advance the spoken and written language development of those affected. In the first experiment (presented in Chapter 2), a comparison of 12 children with CAS, 12 children with inconsistent speech disorder (ISD), and 12 children with typical speech-language development (TD) revealed that children with CAS may be particularly susceptible to phonological awareness and reading deficits. There was no difference in the articulatory consistency and speech severity of the CAS and ISD groups, and no difference in the receptive vocabulary of the CAS, ISD, and TD groups. The children with CAS exhibited poorer phonological awareness scores than the comparison groups and had a greater percentage of participants performing below the expected range for their age on letter knowledge, real word decoding, and phonological awareness normative measures. The children with CAS and ISD performed inferiorly than the children with TD on a receptive phonological representation task. The results showed that the children with CAS had a representational component to their disorder that needed to be addressed in intervention. In the second experiment (presented in Chapter 3), a follow-up pilot study was conducted to examine the long-term effects of a previously conducted intensive integrated phonological awareness programme (7 hours of intervention over 3 weeks) on 2 children with CAS. The children aged 7;3 and 8;3 at follow-up assessment had previously responded positively to the intervention. Results showed that the children were able to maintain their high accuracy in targeted speech repeated measures over the follow-up period. One child was also able to maintain her high accuracy in phonological awareness repeated measures. The children performed superiorly on a standardised phonological awareness measure at follow-up than at pre-intervention. Non-word reading ability showed a sharp increase during the intervention period, while minimal gains were made in this measure over the follow-up period. The findings suggested that an integrated intervention was a potential therapeutic approach for children with CAS. In the third experiment (presented in Chapter 4), the effectiveness of an integrated phonological awareness programme was evaluated for the 12 children (identified in the first experiment) aged 4 to 7 years with CAS. A controlled multiple single-subject design with repeated measures was employed to analyse change in trained and untrained speech and phoneme segmentation targets. A comparative group design was used to evaluate the phonological awareness, reading, and spelling development of the children with CAS compared to their peers with TD over the intervention. The children participated in two 6- week intervention blocks (2-sessions per week) separated by a 6-week withdrawal block. Seven children with CAS made significant gains in their production of trained and untrained speech words with 7 of these children demonstrating transfer of skills to connected speech for at least one target. Ten children showed significant gains in phoneme awareness, and 8 of these children demonstrated transfer of skills to novel phoneme awareness tasks. As a group, the children with CAS demonstrated accelerated development over the intervention period in letter knowledge, phonological awareness, word decoding, and spelling ability compared to their peers with typical development. In the fourth experiment (presented in Chapter 5), the speech, phonological awareness, reading, and spelling skills of children with CAS and TD were re-evaluated 6- months following completion of the intervention programme. A measure of reading accuracy and reading comprehension in a text reading task was administered to the children with CAS. There was no difference in the performance of the children with CAS in post-intervention and follow-up assessments. The children with CAS and children with TD presented with similar relative change in phonological awareness, reading, and decoding measures over the follow-up period. The connected reading performance of children with CAS mirrored their phonological awareness and decoding skills. The findings demonstrated that children with CAS were able to maintain gains achieved during the intervention but may need further support to promote sustained development in written language. In the fifth experiment (presented in Chapter 6), the long-term effects of the integrated phonological awareness programme for identical twin boys who participated in the research intervention at pre-school were examined. The study examined Theo and Jamie's spoken language, phonological awareness, reading, and spelling development during their first year of schooling. The results pointed to the benefit of providing phonological awareness within a preventative framework for children with CAS. Theo and Jamie experienced continued growth in speech and phonological awareness skills. They exhibited age-appropriate reading and spelling development during their first year of formal literacy instruction. It was concluded from this series of experiments that children with CAS are particularly vulnerable to phonological awareness and early reading difficulty, and that an integrated phonological awareness intervention is an effective means of developing speech, phonological awareness, reading, and spelling skills in most children with CAS. The intervention appears to target processes underlying spoken and written language development in this population. The results are discussed within a phonological representation deficit hypothesis of CAS and clinical implications of the findings are highlighted.

The development of phonological representations remains a hot topic within both the developmental and neural network literature. Historically, theoretical accounts have fallen within one of two camps: the accessibility account which proposes that phonological representations are adult-like from infancy (Rozin & Gleitman, 1977; Liberman, Shankweiler & Liberman, 1989) and the emergent account which proposes that phonological representations become gradually restructured over development (Metsala & Walley, 1998; Ventura, Kolinsky, Fernandes, Querido & Morais, 2007; Ziegler & Goswami, 2005). Within this thesis we tested predictions made by the accessibility account and key variants of the emergent account using data from both behavioural (Chapters 2, 3 and 4) and neural network studies (Chapter 5). The novel measures used within Chapters 2 to 4 were devised to allow us to contrast implicit measures of phonological representation (PR) which probe the segmentedness of the representations themselves, with explicit PR measures which tap into children’s conscious awareness of phonological segments. Within Chapter 2 we present evidence that while explicit awareness of phonological structure is dependent on letter-sound knowledge, implicit sensitivity to the segments within words emerges independent of literacy. Within Chapter 3 a longitudinal study investigated the segmentedness of children’s phonological representations at the rime and phoneme level. These results demonstrate that implicit sensitivity to both rime and phoneme segments is driven by vocabulary growth and is not dependent on letter-sound knowledge. The results within Chapter 3 also suggest that, while awareness of rime segments emerges naturally through oral language experience, explicit awareness of individual phonemes is related to letter-sound knowledge. In Chapter 4 we explored the idea of global versus phonemic representation using a mispronunciation reconstruction task. We found that sensitivity to both global and phonemic similarity increased over time, but with global sensitivity reaching adult levels early on in development. In Chapter 5 a neural network was trained on the mappings between real acoustic input and articulatory output data allowing us to simulate the development of phonological representations computationally. The simulation data provide further evidence of a developmental increase in sensitivity to both global and phonemic similarity within a preliterate model. Taken together, the results provide strong evidence that as children’s vocabularies grow they become increasingly sensitive to both the global properties and segmental structure of words, independent of literacy experience. Children’s explicit awareness of phonemes, on the other hand, seems to emerge as a consequence of learning the correspondence between letters and sounds. Within the context of the wider literature, the current results are most consistent with the PRIMIR framework which predicts early detailed phonetic representations alongside gradually emerging phonemic categories (Werker & Curtin, 2005). This thesis underlines the importance of using implicit measures when trying to probe the representations themselves rather than children’s conscious awareness of them. The thesis also represents an important step towards modelling the emergence of segmental representation computationally using real speech data.

The research reported in this thesis examines issues of word recognition in human speech perception. The main aim of the research is to assess the effect of regular variation in speech on lexical access. In particular, the effect of a type of neutralising phonological variation, assimilation of place of articulation, is examined. This variation occurs regressively across word boundaries in connected speech, altering the sUlface phonetic form of the underlying words. Two methods of investigation are used to explore this issue. Firstly, experiments using cross-modal priming and phoneme monitOling techniques are used to examine the effect of variation on the matching process between speech input and lexical form. Secondly, simulated experiments are performed using two computational models of speech recognition: TRACE (McClelland & Elman, 1986) and a simple recun-ent network. The priming experiments show that the mismatching effects of a phonological change on the word-recognition process depend on their viability, as defmed by phonological constraints. This implies that speech perception involves a process of contextdependent inference, that recovers the abstract underlying representation of speech. Simulations of these and other experiments are then reported using a simple recurrent network model of speech perception. The model accommodates the results of the priming studies and predicts that similar phonological context effects will occur in nonwords. Two phoneme monitOling studies support this prediction, but also show interaction between lexical status and viability, implying that phonological inference relies on both lexical and phonological constraints. A revision of the network model is proposed which leams the mapping from the surface form of speech to semantic and phonological representations.

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