Thursday, May 24, 2007

Nonword (Ga/Gsm) repetition tasks - literature to track

Sorry for my very inconsistent posting over the past few months. This summer has been crazy as I work with my lovely fiance to plan a wedding, sell two houses, and build a new house :)

The purpose of this post is to alert readers to a trend I've detected (I may be late in this least I've now noticed it..better late than never)---an increasing body of empirical literature that implicates the abilities measured by non-word repetition tasks in the identification of children with specific language impairments (SLI). Today I ran across a meta-analysis by Estes et al. (2007; click here to view) that continues to highlight the importance of these abilities and measurement tasks. The abstract is reproduced below.

Something important seems to be measured by non-word repetition tasks, although what these abilities are is a matter of debate. As noted by Estes et al.:
  • "There has been considerable debate surrounding the nature of the skills tapped in nonword repetition, whether it recruits phonological working memory (Bishop et al., 1996; Botting & Conti-Ramsden, 2001; Montgomery, 1995b; Van der Lely & Howard, 1993), phonological encoding (Kamhi & Catts, 1986), phonological awareness or sensitivity (e.g., Metsala, 1999), or a general phonological processing ability (e.g., Bowey, 1996, 2001). Many authors have also acknowledged that the act of repeating nonwords involves multiple processes (e.g., Briscoe, Bishop, & Norbury, 2001; Edwards & Lahey, 1998; Gathercole, Willis, Baddeley, & Emslie, 1994; Snowling, Chiat, & Hulme, 1991). A child's ability to repeat a novel word may be affected by any of the component skills involved in the process of hearing, encoding, and producing a word form: the ability to perceive speech distinctions; the preciseness, robustness, or organization of phonological and morphological representations; the ability to store the word form; and motor planning and articulation skills. The impairments of children with SLI may affect performance at any point or at many points in this process."
I concur. Task analysis suggests that, from a CHC factor analysis perspective, non-word repetition tasks may garner their diagnostic sensitivity from their factorial complexity (i.e., they measure multiple important abilities/constructs). These may include such Ga (auditory processing) narrow abilities as phonetic coding (PC), speech sound discrimination (US), memory for sound patterns (UM), and temporal tracking (UK). In addition, clearly the Gsm narrow ability of working memory (MW; what is often called the phonological working memory or articulatory loop) is implicated. Other CHC candidate abilities included efficacy of accessing a person's lexicon (aka; speed of lexical access or naming facility-Glr: NA). For users of the WJ-III battery [conflict of interest disclosure - I'm a coauthor], we have a test called Sound Awareness that has been found to be very predictive of academic achievement and diagnostic classification (normal vs some kind of disorder)...primarily, I believe, because it is a CHC ability-complex measure of multiple narrow abilities (at a minimum, PC and MW). Measures that are not factorially "pure" can still be important and useful for other assessment purposes - diagnosis and prediction.

I would encourage readers to continue to track the emerging non-word repetition practical and theoretical literature. Another important article to read is by Gathercole (2006). Also, I've previously blogged about a non-word repetition article in the journal Dyslexia that, IMHO, suffered from serious methodological flaws and should not be taken seriously. Finally, as my awareness of this literature has grown I recently ran a search of the IAP Reference Database for other articles that may be related (as you will see..there is no shortage of literature to read in this area).

Estes et al. (2007) Abstract
  • Purpose: This study presents a meta-analysis of the difference in nonword repetition performance between children with and without specific language impairment (SLI). The authors investigated variability in the effect sizes (i.e., the magnitude of the difference between children with and without SLI) across studies and its relation to several factors: type of nonword repetition task, age of SLI sample, and nonword length. Method: The authors searched computerized databases and reference sections and requested unpublished data to find reports of nonword repetition tasks comparing children with and without SLI. Results: Children with SLI exhibited very large impairments in nonword repetition, performing an average (across 23 studies) of 1.27 standard deviations below children without SLI. A moderator analysis revealed that different versions of the nonword repetition task yielded significantly different effect sizes, indicating that the measures are not interchangeable. The second moderator analysis found no association between effect size and the age of children with SLI. Finally, an exploratory meta-analysis found that children with SLI displayed difficulty repeating even short nonwords, with greater difficulty for long nonwords. Conclusions: These findings have potential to affect how nonword repetition tasks are used and interpreted, and suggest several directions for future research.
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