Abstract
In verbal working memory, two processes serve to retain a fading memory trace: subvocal rehearsal and lexical redintegration. While recent studies on students with mild and borderline intellectual disabilities (MBID) have yielded mixed results on rehearsal, redintegration has not been researched in MBID, yet. Furthermore, most studies have used a group-matched design which, due to methodological constraints, can only distinguish between two different development patterns. Thus, we study both rehearsal and redintegration in students with MBID using developmental trajectories that have greater potential for identifying differential developmental patterns than traditional group-matching approaches. We investigate whether three aspects in working memory develop differently in students with MBID in comparison to typically developing students: (a) the general capacity of the phonological loop, and the effectiveness of (b) rehearsal, and (c) redintegration. We use three different developmental indicators to compare trajectories: chronological age, cognitive capacity, and vocabulary size. N = 210 students (87 students with MBID, 123 typically developing students) completed working memory span tasks with short and long (1- vs. 3-syllable) real words and pseudowords. The effect for word length (short vs. long) measures rehearsal, and the lexicality effect (real words vs. pseudowords) measures redintegration. Results show that developmental trajectories reveal an intercept difference but no slowed rate in rehearsal, and no impairment in redintegration. However, concerning the developmental relation between redintegration and vocabulary size, students with MBID reveal a differential pattern as redintegration appears higher for students with small vocabulary size, but unexpectedly decreases as vocabulary size increases. We conclude that students with MBID show a delayed onset in the development of capacity of the phonological loop and rehearsal and that they do not catch up in their development. Redintegration does not seem to be impaired in relation to age and cognitive capacity. However, the differential relation of redintegration with vocabulary size calls for further research. While impaired subvocal rehearsal appears to be connected to the developmental problems of students with MBID, lexical redintegration seems to be intact in relation to chronological age and cognitive capacity, making it a possible area of strength.
Highlights
Purpose of the StudyMild and borderline intellectual disabilities (MBID) are defined as deficits in intellectual and adaptive functioning with an IQ between 55–70 and 70–85
Does verbal working memory in students with mild and borderline intellectual disabilities (MBID) develop differently from typically developing students? We examine whether three different developmental indicators can predict the capacity of the phonological loop (PL) and the effectiveness of rehearsal and redintegration processes in students with MBID compared with typically developing children (TD) peers
The aim of this study was to determine whether students with MBID showed differential developmental patterns in three aspects of verbal working memory (WM): (a) the capacity of the PL, (b) the effectiveness of rehearsal, and (c) the effectiveness of redintegration
Summary
Purpose of the StudyMild and borderline intellectual disabilities (MBID) are defined as deficits in intellectual and adaptive functioning with an IQ between 55–70 (mild) and 70–85 (borderline). Most students with MBID have prominent deficits in academic learning. Existing MBID etiology models are often lists of unconnected causal factors, describing the phenomenon only at a vague level (e.g., Schröder, 2000; Kretschmann, 2007; Shaw, 2010 as cited in Hassiotis, 2015), and lacking empirical foundation. Coherent, and comprehensive theories about MBID are lacking. While most theories include cognitive processes and agree that information processing is likely to be impaired, they do not further elaborate on the nature of cognitive processes or the severity of impairment. Without such knowledge, we can neither improve our theories about MBID nor develop effective interventions
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