Syllable structure development of toddlers with expressive specific language impairment

A total of 35 children – 20 with expressive specific language impairment (SLI-E) and 15 typically developing (TD) peers – were compared longitudinally from 24 to 36 months with respect to their production of syllable shapes in 10-minute spontaneous speech samples. SLI-E 24-month-olds predominantly produced earlier developing syllable shapes containing vowels, liquids, and glides. TD 24-month-olds and SLI-E 36-month-olds produced approximately the same proportion of syllable types, with the exception of consonant clusters, where TD 24-month-olds produced more than SLI-E 36-month-olds. TD children at 36 months showed the greatest use of syllable shapes containing two different consonants and consonant clusters. Detailed analyses revealed that SLI-E children produced fewer syllable shapes containing final consonants, more than one consonant type, and consonant clusters. Furthermore, the children with SLI-E were found to vocalize less often than their TD peers. The possible relationships between these findings, SLI-E children’s concomitant deficits in morphology and syntax, and the implications for diagnosis and remediation are discussed. A focus of research in recent years has been on the development of a group of toddlers known as “late talkers.” Late talkers are typically identified as those children who fail to produce at least 50 vocabulary words or any two-word combinations by age 2 (Rescorla, 1989; Rescorla & Schwartz, 1990; Scarborough & Dobrich, 1990), yet who do not demonstrate deficits in hearing, intelligence, or receptive language ability. It is currently estimated that the prevalence of expressive language delay at 24 months is as high as 15% in children from low-income families and 7% in children from middle-class families (Rescorla, 1984). Despite the valuable insight this population may provide into the development of specific language impairment, it has not been particularly well studied. The shortage of data is largely due to the unavailability of assessment tools for toddlers. The relatively recent development of parental checklists, such as the Language Development Survey (Rescorla, 1989) and the MacArthur Com 2000 Cambridge University Press 0142-7164/00 $9.50 Applied Psycholinguistics 21:4 430 Pharr et al.: Syllable structure development municative Development Inventory (CDI) (Fenson et al., 1993), has assisted researchers and clinicians in the early identification of 2-year-old late talkers. Overall, researchers have demonstrated that at least half of late talkers identified by age 2 will be considered language-disordered by age 3 or older (Fischel, Whitehurst, Caulfield, & De Baryshe, 1989; Paul, 1989; Rescorla, Roberts, & Dahlsgaard, 1997; Rescorla & Schwartz, 1990). Some of these children will be diagnosed with expressive specific language impairment (SLI-E). However, the proportion of late-talking children who continue to perform at below-average levels at age 3 differs from study to study and varies based on which outcome measure is used (Rescorla et al., 1997). Typically, at age 3 late talkers have made rapid gains in the areas of lexical development and the ability to explain and describe, but continue to demonstrate persistent and more evident delays in morphology and syntax (Rescorla et al., 1997). Researchers who have examined long-term recovery rates for late-talking toddlers have reported that the majority of these children move into the normal range on all standardized tests by first or second grade (Bishop & Adams, 1990; Paul, 1996; Rescorla, 1993; Whitehurst & Fischel, 1994). Nevertheless, as a group late talkers continue to perform more poorly than their peers, with persistent difficulty in the areas of verbal short-term memory, sentence formulation, word retrieval, auditory processing of complex information, and elaborated verbal expression (Rescorla, 1993). Furthermore, not all children with a history of expressive language delay recover. Paul (1996), for example, reported a recovery rate of only 74% by first grade. Consequently, investigators have attempted to define more clearly the factors that may identify late talkers who will present with persistent difficulties later in life. Most research to date has focused on late talkers’ failure to develop lexical, morphological, syntactic, gestural, and social skills at a rate similar to normally developing peers. Surprisingly few studies have systematically evaluated the phonetic development of these children, although several researchers have noted that articulation development may fall below age expectations (Fischel et al., 1989; Rescorla & Schwartz, 1990; Scarborough & Dobrich, 1990). Phonetic development of late talkers: Current research Over the past decade, a large number of studies of speech-sound development in late-talking and language-disordered children have been published. For ease of discussion, Table 1 provides a summary regarding subject characteristics, assessment protocols, and primary findings. Taken together, the studies cited here collectively found that, when compared to normally developing children, SLI-E children between the ages of 2 and 3 years exhibit reduced phonetic inventories, simpler syllable shapes, and reduced pronunciation accuracy. Unfortunately, the phonetic development of this population has not yet been selectively examined in a longitudinal investigation between the typical age of early diagnosis (24 months) and the age at which more formal testing generally occurs (36 months). The literature to date is characterized by some limitations that indicate further study in this area is warranted: (a) cross-sectional rather than longitudinal design (Paul & Jennings, 1992; Thal et al., 1995); (b) small sample size, with regard to number of subjects and quantity of speech analyzed (Paul & Applied Psycholinguistics 21:4 431 Pharr et al.: Syllable structure development Jennings, 1992; Scarborough & Dobrich, 1990; Stoel-Gammon, 1989); and (c) global rather than specific descriptions of phonological performance (Rescorla & Schwartz, 1990; Whitehurst, Smith et al., 1991). For several years, researchers have noted the uncertain relationships among delayed expressive language, reduced phonetic inventory, and production of simpler syllable shapes (Mirak & Rescorla, 1998; Paul & Jennings, 1992, Rescorla & Ratner, 1996; Stoel-Gammon, 1989; Thal et al., 1995; Whitehurst, Smith et al., 1991). The driving force behind these developmental deficits is as yet unknown, although speculation has led to theories of limited informationprocessing abilities (Leonard, Sabbadini, Volterra, & Leonard, 1988), symbolic capacity (Terrell & Schwartz, 1988), and memory capacity (Kirchner & Klatzky, 1985). However, the continued observation that many SLI-E children display concomitant phonological delays raises interesting questions about the role of phonology in the development of other domains, such as the lexicon and bound morphology. Only intensive and careful research into the precursors of persistent language difficulty will provide clinicians with the tools and information they require to make informed decisions regarding the early identification of, and appropriate intervention for, 2-year-old late talkers. Thus, we posed the following questions: (1) What patterns of syllable structure development do children with SLI-E display between the ages of 2 and 3 years? (2) How do children with SLI-E compare to normally developing agemates during this period of development?