Phonological short-term memory impairment and the word length effect in children with intellectual disabilities

Neurocognitive functioning of children with mild to borderline intellectual disabilities and psychiatric disorders: profile characteristics and predictors of behavioural problems

BACKGROUND

The aim of the current study was twofold: first, to uncover a neurocognitive profile of normative and relative strengths and weaknesses that characterises an extremely vulnerable group of children with mild to borderline intellectual disabilities (MBID) and co-morbid psychiatric disorders, and second, to investigate the relevance of these neurocognitive functions explaining internalising and externalising symptoms.

METHOD

We recruited 45 children (M_age  = 9.5, SD_age  = 1.7; range 6-13 years) with MBID (Full-Scale IQ 50-85) and at least one psychiatric disorder. Neurocognitive functioning was examined utilising the Wechsler Intelligence Scale for Children - Fifth Edition (WISC-V) indices and the Cognitive Task Application (COTAPP), a comprehensive computerised self-paced task designed in such a manner that 'g' (an overall tendency of children with MBID to execute tasks with a slower reaction time and a higher error rate) has been corrected for in the administration of the task (i.e. completely self-paced) and in the operationalisation of outcome measures. Behavioural problems were measured using the CBCL and TRF. One-sample t-tests and binomial tests were carried out to compare performance with normative data. Regression analyses were used to examine the relationship between neurocognitive parameters and mental health.

RESULTS

Compared with normative data, very small to very large effect sizes were found, indicating clear heterogeneity amongst neurocognitive domains relevant for children with MBID. Two prominent neurocognitive weaknesses emerged: processing speed - characterised by slowness and unstableness combined with a high drift rate and delayed processing of the previous trial, particularly under higher cognitive demands - and working memory - in terms of a weaker central executive and 'slave' systems to temporarily store information. Both domains were not clearly predictive of internalising or externalising problems.

CONCLUSION

Children with MBID and psychiatric disorders are hampered by a strongly diminished processing speed and working memory capacity, together resulting in an overall limited processing capacity that may underlie the general developmental delays on domains that depend on fast and parallel processing of information (i.e. language, reading, mathematics and more complex forms of social cognition). Neurocognitive vulnerabilities are neither necessary nor sufficient to explain internalising and externalising problems; rather, a mismatch between the support needs and adaptations these children need, arising from their diminished processing capacity, and the inadequacy of the environment to compensate for this vulnerability may be of relevance.

Acquisition of Reading and Intellectual Development Disorder

We propose a review of the literature of the studies investigating reading acquisition in intellectual deficiency (ID), with particular focus on the explanatory factors for reading difficulties. Indeed, we explore the role of intellectual efficiency, perceptual abilities, oral language development, phonological processing and memory. The study of reading acquisition in ID is a challenge because of a high degree of heterogeneity in the results which, together with other variables influencing learning and development. This review has allowed us to understand that there are multiple reasons why individuals with ID have difficulty learning to read. More specifically, there is a link between reading skills and certain cognitive skills, such as perception, oral language, phonological processing and working memory.

Verbal Working Memory Processes in Students With Mild and Borderline Intellectual Disabilities: Differential Developmental Trajectories for Rehearsal and Redintegration

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.

Evidence of a Phonological Similarity Effect After Rehearsal Training in Adolescents With Intellectual Disability

A phonological similarity effect (PSE) in adolescents with an intellectual disability (ID) has previously been shown with auditory stimuli, but studies using visual stimuli are scarce. In the case of visually presented items, PSE requires verbal recoding before it appears. Using visual items, we trained 15 participants with ID to use rehearsal strategies. Another group of 13 participants took part in nonstrategic training. In both groups, PSE was tested before and after training. Participants in the strategy-training group, who showed no PSE at pretest, began to show such an effect during the training stage and maintained it until posttest as was observed through microgenetic analysis. Participants with ID showing no PSE with visual material can thus be trained to show this effect through extensive use of cumulative rehearsal. Such training would lead them to recode items verbally, which in turn would make phonological similarities more salient and lead to a PSE.

Working memory studies among individuals with intellectual disability: An integrative research review

BACKGROUND

Integrative research review infers generalizations about a substantive subject, summarizes the accumulated knowledge that research has left unresolved and generates a new framework on these issues. Due to methodological issues emerging from working memory (WM) studies in the population with non-specific intellectual disability (NSID) (N=64) between 1990-2014, it is difficult to conclude on WM performance in this population.

AIM

This integrative research review aimed to resolve literature conflicts on WM performance among individuals with NSID and to identify the conditions/moderators that govern their WM performance compared to controls with Typical development.

METHOD/PROCEDURE

We used the six stages of integrative research review: problem formulation, data collection, evaluation, data analysis, results, interpretation and discussion.

OUTCOMES AND RESULTS

The findings indicate two types of moderators that determine WM performance in the population with NSID: Participants' moderators (criteria for matching the ID and TD groups, CA and MA), and task moderators [the three WM components of Baddeley and Hitch's (1974) model and task load]. Only an interaction between the two moderators determines WM performance in this population. The findings indicate a hierarchy (from more to less preserved) in WM performance of individuals with NSID: The visuospatial tasks, then some of the executive functions tasks, and the phonological loop tasks being less preserved. Furthermore, at a low level of control, the performance of participants with NSID was preserved beyond the modality and vice versa.

CONCLUSIONS AND IMPLICATIONS

Modality and MA/intelligence determine WM performance of individuals with ID. Educators should prepare intervention programs take the impact of the two moderators into account.

Strategic verbal rehearsal in adolescents with mild intellectual disabilities: A multi-centre European study

BACKGROUND

There is a long-held view that verbal short-term memory problems of individuals with intellectual disabilities (ID) might be due to a deficit in verbal rehearsal. However, the evidence is inconclusive and word length effects as indicator of rehearsal have been criticised.

AIM & METHOD

The aim of this multi-site European study was to investigate verbal rehearsal in adolescents with mild ID (n=90) and a comparison group of typically developing children matched individually for mental age (MA, n=90). The investigation involved: (1) a word length experiment with non-verbal recall using pointing and (2) 'self-paced' inspection times to infer whether verbal strategies were utilised when memorising a set of pictorial items.

RESULTS

The word length effect on recall did not interact with group, suggesting that adolescents with ID and MA comparisons used similar verbal strategies, possibly phonological recoding of picture names. The inspection time data suggested that high span individuals in both groups used verbal labelling or single item rehearsal on more demanding lists, as long named items had longer inspection times.

CONCLUSIONS

The findings suggest that verbal strategy use is not specifically impaired in adolescents with mild ID and is mental age appropriate, supporting a developmental perspective.

Nonverbal auditory working memory: Can music indicate the capacity?

Different working memory (WM) mechanisms that underlie words, tones, and timbres have been proposed in previous studies. In this regard, the present study developed a WM test with nonverbal sounds and compared it to the conventional verbal WM test. A total of twenty-five, non-music major, right-handed college students were presented with four different types of sounds (words, syllables, pitches, timbres) that varied from two to eight digits in length. Both accuracy and oxygenated hemoglobin (oxyHb) were measured. The results showed significant effects of number of targets on accuracy and sound type on oxyHb. A further analysis showed prefrontal asymmetry with pitch being processed by the right hemisphere (RH) and timbre by the left hemisphere (LH). These findings suggest a potential for employing musical sounds (i.e., pitch and timbre) as a complementary stimuli for conventional nonverbal WM tests, which can additionally examine its asymmetrical roles in the prefrontal regions.

Specific language impairment: a convenient label for whom?

BACKGROUND

The term 'specific language impairment' (SLI), in use since the 1980s, describes children with language impairment whose cognitive skills are within normal limits where there is no identifiable reason for the language impairment. SLI is determined by applying exclusionary criteria, so that it is defined by what it is not rather than by what it is. The recent decision to not include SLI in DSM-5 provoked much debate and concern from researchers and clinicians.

AIMS

To explore how the term 'specific language impairment' emerged, to consider how disorders, including SLI, are generally defined and to explore how societal changes might impact on use the term.

METHODS & PROCEDURES

We reviewed the literature to explore the origins of the term 'specific language impairment' and present published evidence, as well as new analyses of population data, to explore the validity of continuing to use the term.

OUTCOMES & RESULTS AND CONCLUSIONS & IMPLICATIONS

We support the decision to exclude the term 'specific language impairment' from DSM-5 and conclude that the term has been a convenient label for researchers, but that the current classification is unacceptably arbitrary. Furthermore, we argue there is no empirical evidence to support the continued use of the term SLI and limited evidence that it has provided any real benefits for children and their families. In fact, the term may be disadvantageous to some due to the use of exclusionary criteria to determine eligibility for and access to speech pathology services. We propose the following recommendations. First, that the word 'specific' be removed and the label 'language impairment' be used. Second, that the exclusionary criteria be relaxed and in their place inclusionary criteria be adopted that take into account the fluid nature of language development particularly in the preschool period. Building on the goodwill and collaborations between the clinical and research communities we propose the establishment of an international consensus panel to develop an agreed definition and set of criteria for language impairment. Given the rich data now available in population studies it is possible to test the validity of these definitions and criteria. Consultation with service users and policy-makers should be incorporated into the decision-making process.