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|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|33567||2014||13 صفحه PDF||سفارش دهید||محاسبه نشده|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Journal of Fluency Disorders, Volume 39, March 2014, Pages 12–24
Purpose Several empirical studies suggest that children who stutter, when compared to typically fluent peers, demonstrate relatively subtle, yet robust differences in phonological encoding. Phonological encoding can be measured through the use of tasks that reflect the underlying mechanisms of phonological processing, such as phonological awareness. This study investigated the phonological encoding abilities of five- and six-year old children who stutter. Methods Young children who stutter were paired according to language ability, maternal education, and sex to their typically fluent peers. Participants completed multiple measures of phonological awareness abilities (i.e., sound matching, phoneme blending, elision), as well as measures of expressive and receptive vocabulary and articulation. Results Young children who stutter performed significantly less well than nonstuttering peers on tasks of elision and sound blending. No between-group differences were found in sound matching abilities or in any of the background language measures. Conclusions Results suggest that young children who stutter have subtle, yet robust, linguistic differences in certain aspects of phonological encoding that may contribute to an unstable language planning system in young children who stutter.
1.1. Phonological awareness and phonological encoding Some theorists posit that one contributing factor in the production of disfluencies is a difficulty with the underlying selection and preparation of the sounds that form the words in a speaker's message (Howell and Au-Yeung, 2002, Kolk and Postma, 1997, Perkins et al., 1991 and Wingate, 1988). Although details of the psycholinguistic theories of stuttering vary, they all hypothesize that a delay or breakdown occurs when phonological words are constructed from individual phonemes, that is, during the process of phonological encoding (Howell and Au-Yeung, 2002, Kolk and Postma, 1997, Perkins et al., 1991 and Wingate, 1988). The theoretical construct of phonological encoding has been conceptualized differently in various models of typical language formation. Some models, such as the Gestural Linguistic Model (Browman and Goldstein, 1992, Browman and Goldstein, 1997 and Saltzman and Munhall, 1989), suggest that the process of phonological encoding is closely related to speech motor production. Other models, such as WEAVER++ (Levelt, 1989, Levelt et al., 1999 and Roelofs, 2004), posit that phonological encoding is a process that occurs before the speech motor system is activated. Both of these models include a process of phonological encoding, but the execution of this process is envisioned in different ways. The impetus for this current line of research has its basis in psycholinguistic theories of stuttering, thus, this article uses the definition of phonological encoding as forwarded by WEAVER++ (Levelt et al., 1999 and Roelofs, 2004). WEAVER++ defines phonological encoding as the process by which the phonological code (i.e., phonemes or syllables) of a word is retrieved and reassembled in an incremental, just-in-time manner to allow for efficient construction of phonological words. The process of phonological encoding is one that is obscured from direct observation because it is deeply embedded in the process of language formulation (Coles et al., 1995 and Meyer, 1992) and must therefore be explored through alternate processes that reflect its incremental nature. One aspect of phonological encoding that can be observed is the process of phonological awareness, which is an individual's ability to identify, isolate, and manipulate various-sized segments of speech such as words, syllables, onsets/rimes, and individual phonemes. Phonological awareness skills begin to stabilize around age five, allowing for exploration of the phonological encoding abilities of young children who stutter as close to the onset of stuttering as possible once phonological awareness skills are established. Performance on phonological awareness tasks also parallel the processes that occur during phonological encoding, thus providing a valuable research tool in this empirical investigation of the phonological encoding skills of children who stutter. 1.2. Phonological awareness Phonological awareness tasks are well understood and frequently used with preschool and school-age children (see reviews in Gillon, 2004, Sodoro et al., 2002 and Troia, 1999). These abilities progress along a developmental continuum from less-to-more complex. Rhyming, sound matching, and phoneme blending abilities develop first, followed by later developing skills such as phoneme segmentation, elision and phoneme reversal (Adams, 1990, Gillon, 2004 and Schuele and Bourdreau, 2008). Rhyming involves the determination of whether two words rhyme (e.g., “Which word rhymes with cat? Cake, tin, or mat?”). Sound matching tasks measure whether the child can identify individual phonemes and match the occurrence of those phonemes in sets of words (e.g., “Which word starts with the same sound as pen? Pot, hat, or cane?”) Phoneme blending requires an individual to hear syllables or individual phonemes and blend them together to create a word (e.g., “What word do these sounds make? pa–per”). Phoneme segmentation measures an individual's ability to break apart the phonetic code of a word to identify and produce the constituent phonemes of that word (e.g., “Say the word dog one sound at a time. d-o-g”). Elision is the ability to remove a phonetic segment from a given word to create a brand new word. This requires the individual to not only break apart the phonemes of a given word, but also blend the remaining phonemes together to make a new word (e.g., “Say plants without saying/l/. pants”). Finally, phoneme reversal is a task that asks the individual to hear a word and then break apart the phonetic code so it can be reassembled in the reverse order, creating an entirely new word (e.g., “Say/tif/backwards. feet”). Five- and six-year old children are capable of completing tasks like rhyming, sound matching, and phoneme blending that use earlier-developing skills, while tasks like phoneme segmentation and phoneme reversal are typically established later ( Gillon, 2004). Where a child falls along the developmental continuum should be considered when administering phonological awareness tasks to prevent inadvertent skewing of the outcomes due to developmentally inappropriate tasks. Just as phonological awareness abilities emerge in a sequence from less-to-more complex, the stimuli used in each phonological awareness task can also be manipulated in terms of complexity. A less complex task such as phoneme blending can include stimuli that range from simple (e.g., “blend/k-æ-t/ → cat”) to more complex (e.g., “blend/i-m-ɝ-ʤ-ɛ-n-s-i/ → emergency”). This is accomplished through the modification of the number of phonemes or syllables as well as the presence or absence of consonant clusters. Tasks containing more phonemes and syllables are more difficult to complete as there are more phonemes to identify, sort, or blend and must be held in working memory ( Sevald, Dell, & Cole, 1995). The level of phonological complexity of the stimulus items will increase in difficulty with the presence of consonant clusters ( Sasisekaran & Weber-Fox, 2012), as well as the inclusion of later developing phonemes ( Moore et al., 2010 and Storkel, 2001). Thus, both task and stimuli complexity should be considered when assessing phonological awareness abilities. 1.3. Phonological representations Phonological representations in young preschool children are initially stored in holistic form, that is, “without detailed phonological segmentation” (Brooks & MacWhinney, 2000, p. 337). They then gradually undergo a developmental shift toward incremental representations that support just-in-time phonological encoding (Brooks and MacWhinney, 2000, Jusczyk, 1997, Metsala, 1999 and Walley, 1993). The shift of phonological representations from holistic to incremental representations begins around age five and continues to refine until approximately age eleven (Brooks & MacWhinney, 2000). This growth occurs at roughly the same time that phonological awareness skills begin to develop and appears to parallel vocabulary growth as well (de Cara and Goswami, 2003, Jusczyk, 1993, Metsala and Walley, 1998 and Nittrouer, 1996). During the initial stages of development, a child's awareness is implicit: there is some level of understanding of sentences and words, but a child cannot isolate or identify these segments volitionally ( Carroll et al., 2003 and Gombert, 1992). As children mature, phonological awareness expands to include not only large phonemic units, such as sentences and words, but also includes an awareness of more fine-grained phonemic representations, such as syllables and individual phonemes. Thus, phonological awareness in older children and adults is explicit: they are able to volitionally identify, segment, and manipulate words down to the smallest constituent sound ( Anthony and Lonigan, 2004, Treiman and Zukowski, 1991 and Treiman and Zukowski, 1996). These evolving processes have particular relevance to the development of fluent speech. For example, Byrd, Conture, & Ohde (2007) demonstrated that five-year-old children who stutter appear to retain more immature holistic representations, while age-matched peers who do not stutter have shifted to more mature, and theoretically more efficient, incremental representations. If children who stutter maintain use of holistic representations longer than their non-stuttering peers, then the ability to segment phonological representations might be impaired as well. A strong, positive correlation exists between expressive vocabulary and performance on phonological awareness tasks (Cooper, Roth, Speece, & Schatschneider, 2002). Therefore, performance on phonological awareness tasks can be influenced by general language and vocabulary ability. For example, if a child has strong expressive language skills, it is likely that the child also possesses strong phonological awareness skills. Conversely, a child with reduced expressive language abilities will possess reduced or depressed phonological awareness abilities. This indicates that there are potential moderating factors that may affect the outcome of a child's performance on phonological awareness tasks. Care must be taken to account for the potential contribution of language ability when exploring phonological awareness abilities and ensure that the participants in studies of phonological awareness are well matched on these abilities to lessen the possible contribution of the language abilities. 1.4. Stuttering and phonological awareness Few studies have cited phonological awareness as a specific aim of investigation with individuals who stutter. Yet, closer examination of many recent studies of phonological encoding reveal that the tasks used could be characterized as phonological awareness tasks (e.g., rhyme monitoring, phoneme monitoring, segmentation). Studies have investigated phonological encoding using phonological awareness tasks with adults (Byrd et al., 2012b, Sasisekaran and De Nil, 2006, Sasisekaran et al., 2006 and Weber-Fox et al., 2004) and school-age children (Bajaj et al., 2004, Sasisekaran and Byrd, 2013, Sasisekaran et al., 2013 and Weber-Fox et al., 2008), although not all of the studies have reported differences (Bajaj et al., 2004). Of these studies, the authors are aware of only one that has included some young children who stutter, along with some school-age children, as participants in their investigation of phonological awareness abilities (Bajaj et al., 2004). Studies with young children who stutter provide an interesting opportunity to allow measurement of abilities closer to the onset of stuttering, yet it is unknown which young children who stutter will persist into adulthood or will recover. The children who persist in stuttering may possess different abilities than those who develop into typically fluent speakers, which make direct comparison of studies with school-age and preschool children difficult to interpret. No prior study has exclusively investigated these abilities in young children who stutter, but we can gain some insight from those with school-age participants. Bajaj et al. (2004) investigated phonological awareness in 46 children who stutter and their nonstuttering peers. Participants ranged in age from 5:10 to 8:10; thus, only a portion of the participants in this study could be considered preliterate children. The phonological awareness tasks included administration of The Lindamood Auditory Conceptualization Test (LAC; Lindamood & Lindamood, 1979), which requires phoneme identification and manipulation, as well as the Phoneme Reversal subtest of the Comprehensive Test of Phonological Processing (CTOPP; Wagner, Torgesen, & Rashotte, 1999). Bajaj et al. reported no significant between-group differences in performance on the three phonological awareness tasks. This study utilized three different phonological awareness tasks; however, when considering the developmental progression of phonological awareness, the tasks selected by the authors might not have been developmentally appropriate for all participants ( Schuele & Boudreau, 2008). Phoneme reversal is considered a more developmentally advanced ability that requires the use of greater memory resources than are used when the sound matching task is conducted ( Gillon, 2004 and Schuele and Bourdreau, 2008). The CTOPP manual indicates that the phoneme reversal task is recommended for children seven and older ( Wagner et al., 1999), suggesting that the task may have been too difficult for approximately half the participants in Bajaj et al.’s study (i.e., children in kindergarten and first grade). Conversely, the sound matching task may have been too developmentally simple for the older children ( McBride-Chang et al., 1997 and Wagner et al., 1999). Without access to the original data, it is difficult to determine if these factors might have masked a potential difference. Bajaj et al. were careful to note that their study only examined a few components of phonological awareness and suggested that further exploration would be warranted to come to a full conclusion regarding the phonological awareness skills of children who stutter. Sasisekaran and Byrd (2013) investigated nine school-age children who stutter, matched for chronological age and sex, to nine nonstuttering peers. The children ranged in age from 7 to 13. The participants completed phoneme monitoring and rhyme monitoring tasks in single syllable words and nonwords. The complexity level of the monosyllabic stimuli was manipulated by asking the participants to monitor for phonemes that were embedded in a consonant cluster, which is a developmentally harder task to complete. Receptive vocabulary, working memory, and phonemic awareness are all variables that are known to influence performance on phonological awareness tasks. Thus, participants were also administered the Peabody Picture Vocabulary Test – 4th Edition to measure receptive vocabulary, forward and backward digit span from Weschler's Memory scale as a measure of short-term memory, and the LAC as a measure of phonemic awareness. No between-group differences were reported on these measures. Sasisekaran & Byrd reported that both groups of children took longer to identify the target phoneme if it was embedded within a consonant cluster (increased complexity), but the authors reported that children who stutter required a longer period of time than their nonstuttering counterparts to determine if the phoneme was present. Although no significant between-group differences in response times were reported for either task, a re-examination of the data by the authors revealed that the older participants performed at ceiling on these tasks, while the younger children who stutter took longer to respond than their typically fluent peers. Sasisekaran & Byrd interpreted their findings as an indication that the phonological encoding of children who stutter is not frankly disordered but that subtle differences were beginning to emerge as the task complexity increased. Sasisekaran et al. (2013) conducted a similar phoneme monitoring study with nine school-age children who stutter (age 10 to 14 years), matched on age and sex, to nine nonstuttering children. Expressive and receptive vocabulary, working memory, articulation, and phonemic awareness were all measured, in addition to the investigation of phoneme monitoring in two syllable words. Contrary to the findings reported by Sasisekaran and Byrd (2013), there were significant between-group differences in the phoneme monitoring task, and the measure of phonetic awareness, the LAC. The significant difference reported for the phoneme monitoring may have been due to the increase in stimuli complexity through the use of two-syllable words which increases the level of difficulty of the task. Alternatively, the reduced performance of the children who stutter in the phoneme monitoring task may have been secondary to differences in phonemic awareness abilities as indicated by the LAC, or a combination of both. Continued research in this area, with particular attention paid to the complexity level of stimuli and tasks, is therefore warranted if researchers are to better understand whether phonological awareness may play a role in the production of disfluencies and the development of stuttering. The aim of the present study was to compare the phonological encoding abilities of 5 and 6 year-old children who stutter and their typically fluent peers by measuring their performance on a diverse range of developmentally appropriate phonological awareness tasks. The theoretical implication of phonological encoding, combined with the initial evidence that phonological awareness is different in school age children who stutter, suggests that further investigation into the phonological awareness abilities of children who stutter may contribute to our understanding of the role phonological encoding may play in the development of stuttering.
نتیجه گیری انگلیسی
A number of theories of stuttering have suggested that one potential cause for disfluencies is a difficulty with the underlying selection and preparation of the sounds that form the words in a speaker's message (Howell and Au-Yeung, 2002, Karniol, 1995, Perkins et al., 1991, Postma and Kolk, 1993 and Wingate, 1988). The differences in phonological awareness and phonological encoding reported here are robust, yet subtle, indicating that when combined with other factors, such as motoric, linguistic, or cognitive abilities the phonological processing systems of children who stutter may become overwhelmed and result in stuttered speech. In addition to contributing to the existing phonological awareness research, the results from the present study also support current psycholinguistic theories that argue that some aspect of phonological encoding is delayed or disrupted in people who stutter.