مهارت های آواشناسی و سطوح عدم تسلط در کودکان پیش دبستانی که لکنت زبان دارند

The relation between stuttering and aspects of language, including phonology, has been investigated for many years. Whereas past literature reported that the incidence of phonological difficulties is higher for children who stutter when compared to normally fluent children, the suggestion of association between the two disorders also drew several critical evaluations. Nevertheless, only a limited amount of information exists concerning the manner and extent to which the speech sound errors exhibited by young children who stutter, close to stuttering onset, is related to the characteristics of their stuttering, such as its severity. Conversely, information is limited regarding the effects a child's phonological skills may have on his/her stuttering severity. The current study investigated the mutual relations between these two factors in 28 carefully selected preschool children near the onset of their stuttering. The children, 20 boys and 8 girls, ranged in age from 25 to 38 months, with a mean of 32.2 months. The phonological skills of two groups with different ratings of stuttering were compared. Similarly, the stuttering severities of two groups with different levels of phonological skills (minimal deviations–moderate deviations) were compared. No statistically significant differences were found for either of the two factors. Inspection of the data revealed interesting individual differences.

The reader will be able to list: (1) differences in the phonological skills of preschool children whose stuttering is severe as compared to children whose stuttering is mild and (2) differences in stuttering severity in preschool children with minimal phonological deviations as compared to children with moderate phonological deviations. The relation between stuttering and linguistic aspects, including phonology, has been investigated for many years. Although the scientific literature makes frequent reference to a wide range of disorders that are present concomitantly with childhood stuttering (e.g., Arndt & Healy, 2001; Blood & Seider, 1981), much of this work has concentrated on the accompanying language and speech disorders of young children who stutter (see reviews by Bernstein-Ratner, 1997, Louko, 1995, Nippold, 1990, Nippold, 2001, Nippold, 2002 and Nippold, 2004; Watkins, Yairi, & Ambrose, 1999). A number of these studies have emphasized a relation specifically between stuttering and either delayed or different phonological development, suggesting that of all the speech–language problems that co-occur with stuttering, phonological difficulties1 are the most common (Bloodstein, 1987; Cantwell & Baker, 1985; Louko, Edwards, & Conture, 1990; St. Louis & Hinzman, 1988; Paden, 2004; Wolk, Edwards, & Conture, 1993). A majority of past research has focused on the incidence of disordered phonology in children who stutter, resulting in considerable disagreement regarding estimates. At the high end, St. Louis and Hinzman (1988) reported from 66 to 71% of 48 children who stuttered exhibited mild to moderate deviations in articulation, whereas according to more conservative low-end estimates, it appears likely that the co-occurrence is greater than the 2–6% expected in the general population (Beitchman, Nair, Clegg, & Patel, 1986; Hull, Mielke, Timmons, & Willeford, 1971). Thus, Wolk et al. (1993) concluded that, on average, 30–40% of children who stutter also exhibit disordered articulation or phonology. Previous research into possible links between stuttering and delayed or different phonological development has included studies that approached this topic from different angles. These have included investigations into: (a) the correlation between the frequency of disfluencies with the number of phonological errors (Louko et al., 1990, Ryan, 1992 and Ryan, 2001; Yaruss & Conture, 1996); (b) the stuttering behavior of children with normal and disordered phonology (Wolk et al., 1993; Yaruss, LaSalle, & Conture, 1998); (c) the phonological behaviors of children who stutter and normally fluent children ( Wolk et al., 1993); (d) phonological complexity/difficulty (e.g., syllable shape and length; location in utterance) and stuttering ( Howell & Au-Yeung, 1995; Throneburg, Yairi, & Paden, 1994); (e) the relation between the development of stuttering and phonological skills ( Paden & Yairi, 1996; Paden, Yairi, & Ambrose, 1999; Ryan, 2001; Yairi, Ambrose, Paden, & Throneburg, 1996). Although relatively recent reports have raised arguments to shed doubts about the extent and strength of a stuttering–phonology link that must be considered in assessing current beliefs (Nippold, 1990, Nippold, 2001 and Nippold, 2002), findings yielded by the University of Illinois Stuttering Research Program into the co-occurrence of stuttering and phonology provide rationale for continuation of research in this area. Those findings suggest that subtle phonological difficulties, presented at the very early stage of stuttering of preschool children, may be associated with the eventual course of the disorder, that is, whether the children's stuttering persisted or later disappeared. Paden and Yairi (1996) used the Assessment of Phonological Processes—Revised ( Hodson, 1986) to examine the early phonological differences of 36 children, 12 whose stuttering eventually persisted, 12 who eventually recovered early, 12 who eventually recovered after a longer period, and 12 controls. The mean ages were 47.2, 36.7, and 38.3 months, respectively. The examinations were performed soon after onset. Classification into the respective groups was possible after many months of longitudinal follow-ups. Results showed that close to stuttering onset, the group who eventually persisted differed significantly from normally fluent control subjects on the overall mean percentage of error score as well as scores on specific phonological patterns. Scores of the two groups who eventually recovered and their matched controls, however, did not differ significantly. This research was expanded by Paden et al. (1999), employing a much larger sample and more comprehensive procedures. Again, such explorations were made at the first visit when the children were close to the onset of stuttering and still not identifiable as to the future course their stuttering would take. Of the 84 children, 22 were observed to persist in stuttering for at least 48 months after onset (persistent group), whereas 62 had recovered without clinical intervention before that time (recovered group). The two groups were compared, soon after stuttering onset (mean age 42.5 and 33.8 months, respectively), on a number of phonological characteristics, including mean percentage of error, relative levels of severity of phonological impairment, error on specific phonological patterns, progress in the development of key patterns, and the children's strategies for coping with unmastered patterns. Results indicated that the groups whose stuttering would be persistent had poorer mean scores on each of the measures than did the children who would recover from stuttering. One year after the first visit, however, both groups showed progression in phonological development that followed the expected order, and they resorted to typical strategies when patterns had not yet been acquired. The persistent group was progressing more slowly. In yet another study, Paden, Ambrose, and Yairi (2002) examined the phonological progress of the same 84 children, 1 and 2 years later. Results of the assessment at the 1-year follow-up visit showed that the mean difference between the two groups of children was no longer significant. The children whose stuttering would persist had improved phonologically more than those who would recover from stuttering. At the 2-year visit, the mean percentage of phonological error for the two groups was identical. Whereas the Paden and Yairi (1996) and Paden et al., 1999 and Paden et al., 2002 studies had as their focus the relation between the development of stuttering (persistency versus recovery) and development of phonological skills, the Louko et al. (1990) study compared the phonological processes exhibited by children who stutter to those exhibited by their normally fluent peers and correlated the frequency of disfluencies with the number of phonological processes produces. Participants included 30 children who stuttered (mean age = 54 months) and matched control group of normally fluent children. Phonological processes observed for children's spontaneous speech were identified. The children who stuttered, as a group, exhibited a total of 18 different phonological processes, while their controls exhibited only 11 processes. Twelve (40%) of the 30 stuttering children exhibited disordered phonology, defined as either two age-inappropriate or “atypical” phonological processes, as compared to just 2 children in the control group. None of the findings, however, were statistically significant, and children with more severe stuttering were not necessarily using a greater number of phonological processes than those with milder stuttering. It should be noted that participants in this study were appreciably older than those used in the Illinois studies and, thus, were more likely to have stuttered for longer period. Moreover, the older the children in the group, the greater is the percentage of boys and, hence, the greater the likelihood of finding higher percentages of phonological difficulties. The nature of phonological deficits vary with age, as children who are 3 years old typically present quite different phonological abilities from those who are 5 years old. Additionally, the method of evaluating phonological competency was different in the Louko et al. (1990) than in the Illinois studies. One of the most compelling questions concerning a possible stuttering–phonology connection is the mutual consequence of the degree to which the two domains (disfluency and phonological skills) are affected. Among the previous investigations, the Wolk et al. (1993) and Yaruss and Conture (1996) studies are the primary ones that examined the stuttering behavior of children with normal and disordered phonology and the phonological behaviors of children who stutter and normally fluent children. Wolk et al. (1993) reported no statistically significant differences in either the frequency or severity of stuttering in children who stutter with or without concomitant phonological disorders, defined by the authors as at least two age-inappropriate phonological processes or one or more processes that are not typical of normal development. A similar study by Yaruss and Conture (1996) included 3–6-year-old children with a history of stuttering of up to 3 years and a mean of almost 2 years. One group exhibited stuttering and normal phonological abilities while a matched control group evidenced stuttering and disordered phonology, using the same phonological criteria specified in Wolk et al. (1993). No differences were found between the groups in the frequency or duration of disfluencies that occurred in conversational speech. Similarly, the correlation between the number of phonological errors and the number of within-word disfluencies was not statistically significant. Based on information, such as participants’ age, provided in past reports, there are good reasons to believe that many of the children in those studies had been stuttering for 2–3 years or even longer when their phonology and stuttering were assessed. The results of these studies, then, may not accurately reflect the relation between the two disorders at their earlier stages. The length of the stuttering history (post-onset interval) is critical, as we do know that both phonological skills and stuttering change as a function of time. Influenced by many factors, as children grow older, their stuttering may increase or decline and its pattern may be altered. It may completely remit in the majority of them within 1–3 years after onset (e.g., Yairi & Ambrose, 1999). Hence, it is likely that past studies concerning the suggested stuttering–phonology link have missed significant percentages of children who ever stuttered, reporting data that pertain to only a small subset of children who were following the path of persistent, chronic stuttering. Also, in terms of phonology, there are solid grounds for the expectation that a child's phonological skills will change (mostly improve) with age as he/she gets further away from stuttering onset. In short, a delay of even several months results in the exclusion of a large percentage of children who had already recovered from stuttering or who had outgrown early phonological deficiencies. There is an additional epidemiological consideration as both Yaruss and Conture (1996) and Wolk et al. (1993) had only boys as subjects. It is widely known that more males than females stutter and that the male-favored gender ratio increases with age from about 2:1 at the time of onset to 4:1 or 5:1 in older children and adults (Bloodstein, 1995). There is evidence that an important reason for the increased ratio is a higher recovery rate for females (Bloodstein, 1995; Yairi and Ambrose, 1992 and Yairi and Ambrose, 1999). In other words, samples of older children who stutter may consist of appreciably greater proportions of males than what is found at onset. Additionally, the gender ratio also plays an important role in phonological development. At young ages, males are more prone than females to exhibit phonological deficits and their phonological skills progress more slowly as well (Smit & Hand, 1997). In view of these facts, a sample of older children who stutter, consisting of all, or unusually high percentage of, males may incorrectly evidence a higher incidence of phonological difficulties than the normal population simply by virtue of the gender ratio (Yairi, 1999). It appears, therefore, that past research into the phonological behaviors of children who stutter and the stuttering behaviors of children with phonological delays or differences may have overlooked certain epidemiological factors such as natural recovery, gender distribution, and post-onset interval. The need to consider these factors was reinforced in the aforementioned series of studies concerning the phonological skills of preschool children close to stuttering onset by Paden and Yairi (1996) and Paden et al., 1999 and Paden et al., 2002. The dynamics of early stuttering may hold many clues as to the etiology of the disorder. Yet, in spite of the fair amount of research, information is limited about the manner and extent to which the phonological deficiencies exhibited by some young children near stuttering onset co-vary with the characteristics of their stuttering, and, if indeed the two factors co-exist, which one of them has a stronger influence on the other. As stated earlier, one of the questions regarding the relation between the two domains concerns the extent, or degree, to which they are affected. That is, what effect does the severity of stuttering have on phonological performance? Conversely, what influence does the level of phonological ability have on the severity of stuttering? If indeed these communication difficulties are related, it would be logical to expect that children who exhibit severe stuttering also exhibit more phonological deficits and vice versa. If the factors are independent, there would not be such a covariance. Whereas previous investigations have considered factors such as stuttering severity and phonological status, there have not been investigations into the stuttering severity and phonological status of very young children who stutter near stuttering onset. Thus, if there is some validity to the proposed co-occurrence with phonological delays or differences, it may be of great interest. This line of inquiry may be relevant in that it could illuminate the relation and possible developmental asynchrony between phonological proficiency and fluency during the time when stuttering begins. Additionally, by looking at the possible differences in phonological skills between children with mild and severe stuttering, as well as the differences in stuttering severity between children with minimal and moderate phonological deviations, more information can be gained about the possible mutual effects of stuttering on phonological skills. One important motivation for exploring the relation between phonological skills and stuttering is the overlap of children's most common age of stuttering onset (between 2 and 4 years of age) with the period when a child's development is advancing rapidly in almost every capacity, including language, and phonological skills (Bernstein-Ratner, 1997 and Yairi, 1983). To these we can also add the rapid development, at the same time, of the child's anatomy and physiology involved in speech. The associations and co-influences among the developing speech and language domains make it logical to assume that any interference with normal development or progress in one aspect could have multiple effects (Watkins & Yairi, 1997). Such co-occurrence of developmental processes has given rise to the hypothesis that when difficulties with fluency co-occur with difficulties with phonology, the two domains share common etiologies or the presence of one facilitates the appearance of the other (Paden et al., 2002). Speech often is viewed as the product of a series of processes that are taking place simultaneously at several levels (Levelt, 1989). Speech output results from incremental planning at numerous stages, with latter parts of an utterance being planned while earlier parts are being articulated, an idea expressed by Fry in 1969, and then echoed by Garrett (1975), Levelt (1989), and Howell (2002). This has been referred to as a “staged and feedforward” process (Levelt, Roelofs, & Meyer, 1999).2 After the stage of conceptual preparation, word generation proceeds through lexical selection, morphological and phonological encoding, phonetic encoding, and articulation itself. Such hypothetical constructs of lexical access form the crux of recent models as the WEAVER++ (Word-form Encoding by Activation and Verification; Levelt et al., 1999) and the EXPLAN (cognitive planning [PLAN] and articulatory execution of speech [EX]; Howell, 2002). The multi-level, segmented system of speech planning and production raises questions as to how each subsystem can be protected from interferences by other parts of the system. In both of the above models, it could be said that fluency failures arise because of disparity between time available for planning and time available for execution. In other words, as suggested by Fry (1969), if a level of the speech production system goes too fast, speech errors result; if it goes too slowly, hesitations result. In either situation, the speech production system may be out of sync. Stuttering, then, may be regarded as a disorder of mistiming between motor planning and execution, when a child's fluency generating system is tenuous and may not be adequately protected from concurrently performed cognitive processing or competing interferences (i.e., phonological difficulties). If the purpose of the “binding and checking” mechanism involved in normal speech production is to prevent any speech error (Levelt et al., 1999), then perhaps this mechanism is flawed in young children who stutter, leading to a higher incidence of phonological difficulties in this population. Furthermore, if word production is initiated only after all of its syllables have been phonetically encoded (Levelt & Wheeldon, 1994), one may ask what happens when there is an encoding error? For a child who stutters, this may place an additional burden on the task of producing fluent speech. In other words, difficulties involving the timing of the phonological planning/encoding system may indeed cause stress within the fluency generating system, or vice versa. Furthermore, speech error data suggest that the phonological encoding process may be slower for all children as compared to adults (Yaruss & Conture, 1996), and that children's phonological encoding processes may be functionally slower. This may be due to a greater number of perseveratory substitutions as opposed to anticipatory substitutions compared to adults, as well as children's greater error rates overall (Dell, Burger, & Svec, 1997). Whereas normally fluent children apparently develop phonological skills fast enough to accommodate their growing communicative needs, some children who stutter may develop these skills later and may not yet have developed the normal perceptual system to detect errors when they occur (Levelt et al., 1999). Similarly, the Covert-Repair Hypothesis (Postma & Kolk, 1993) postulates that speech difficulties of people who stutter result from problems in pre-motor phonological encoding, wherein the speaker attempts to correct speech errors. Here, stuttering is seen as a covert or internal repair reaction to some flaw in the movements that are required for speech. When a movement is detected as being incorrect, through proprioceptive and then tactile feedback, speech is interrupted before any perceptually identified distortion of speech has occurred (Yaruss & Conture, 1996). In light of the above, findings from the research of Paden and Yairi (1996) and Paden et al., 1999 and Paden et al., 2002 provided some evidence for at least mild delays in phonological development for children who stutter. A working hypothesis guiding this study was that early, sub-clinical phonological delays or differences in development may reveal clues as to the onset and/or trajectory of stuttering. One of the goals of the study was to evaluate in detail whether asynchronies or close parallels in development between stuttering and phonology were evident (e.g., severe stuttering paired with strong or weak phonological development). The study was designed to provide a close analysis of phonological skills in conjunction with the level of disfluency development, near stuttering onset, before the time when the children's stuttering will ultimately diverge into persistent and recovered pathways. The specific questions of the study were as follows. Near the onset of stuttering: (1) Are there differences in the phonological skills of children whose stuttering is severe as compared to children whose stuttering is mild? (2) Are there differences in stuttering severity in children with minimal phonological deviations as compared to children with moderate phonological deviations? The unique contributions of this study are the availability of data about phonological skills and fluency very near stuttering onset and a participant population carefully selected based on epidemiological considerations.