Are items actively removed from working memory during free time in children with developmental language disorder?

Children with developmental language disorder (DLD) have deficits in verbal and non-verbal processing relative to typically developing (TD) peers, potentially reflecting difficulties in working memory, processing speed and inhibition of interference. We examined working memory in children with DLD using the serial-order-in-a-box-complex span (SOB-CS) interference-based model, which posits a time-based mechanism, free time, that governs how interference affects processing performance.

(1) To determine the degree to which children with DLD and TD children differ in the amount of free time available during working memory tasks, and whether potential group differences in free time differ depending on the domain of task demands? (2) To determine the relationship between free time and interference effects on working memory accuracy in children with DLD relative to TD peers.

We examined the relationship between free time and working memory in children aged 9-13 years with DLD relative to age-matched TD peers. Working memory tasks involved five conditions that varied verbal versus non-verbal task demands in an interference processing phase relative to a recall test phase. Free time was the time between response on the interference processing task and onset of the recall test phase.

DLD and TD groups did not differ in total free time in any condition. Results indicated group differences in the relationship between free time and accuracy in the conditions involving verbal recall, but not non-verbal recall. In the verbal-only condition, relatively more free time was associated with worse accuracy for the DLD group, but with better accuracy for the TD group. In the condition with verbal recall paired with non-verbal interference processing, relatively more free time was associated with better accuracy for the DLD group, but not for the TD group.

The overall findings suggest that free time between cognitive operations is positively associated with working memory for both verbal and non-verbal recall, except in the presence of high verbal interference for the DLD group (i.e., verbal interference paired with verbal recall). This finding may reflect poor encoding and attention under particularly challenging verbal processing demands for the DLD group. This study also demonstrates the importance of considering the interrelationships between processing speed and interference in working memory performance.

What is already known on the subject DLD is characterized by core deficits in verbal processing, but also deficits in non-verbal processing. Processing-based hypotheses of DLD-limited verbal working memory, slowed processing speed and inefficient inhibition-do not fully account for behavioural profiles in DLD when considered separately, yet there is evidence suggesting interrelationships among these factors. What this paper adds to existing knowledge The current study tests the key mechanism posited by a theoretical framework that has the potential to integrate these processing-based hypotheses. Our findings indicate that the effect of this mechanism differed in DLD relative to TD peers in the presence of high verbal task demands. Our findings also demonstrate the importance of considering the interrelationships among cognitive processes in children with DLD. What are the potential or actual clinical implications of this work? In practice, results from the current study suggest that children with DLD may benefit from supplementing verbal information with non-verbal information and from pauses between successive presentations of verbal information. These strategies may support their ability to maintain and act on information during verbal processing.