Relationship between gains in working memory and syntax

Finally, whether or not the gains made in WM were related to the increase in the degree of syntactic complexity found in DLD children in the WM training group was investigated, but analyses revealed no significant correlation between these two variables. In other words, while children with DLD who participated in the WM training group showed significant improvement

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in both WM and in syntax, these improvements do not seem directly related, or may not have been motivated by the same primary cause. This indicates that large progress on the post-training WM tasks was not a necessary condition in order for large progress to be made on the post-training syntax task. This seems unexpected, but we offer a possible explanation.

For starters, the conception and design of Magic Memory are firmly based on empirical findings related to WM development and language acquisition, but it is widely accepted that WM is sustained by an ensemble of attentional and executive processes, in particular selective attention (Majerus, Leclercq et al., 2009; Veer, Luyten, Mulder, van Tuijl, & Sleegers, 2017). It is thus necessary to better understand exactly which underlying cognitive processes are being trained with our training program. Our study was conceived within the Derivational Complexity Hypothesis (DCH) theoretical framework (Jakubowicz, 2011) with the idea that our WM training program would make available more processing resources and that this in turn would lead to the production of more complex syntax. However, it is possible that an intensive training program, such as the one proposed with Magic Memory that requires 30 minutes of sustained attention to complete each session²⁸, not only increases the size of the computational workspace of WM but also exercises the attentional mechanisms related to WM. In other words, the gains made in syntax could be due to gains made in WM, as proposed by the DCH, although at this time such a relationship is unclear from our data. Alternatively, the gains made in syntax could be due to gains in more general, underlying processes, such as attention. Indeed, a number of WM models include an attentional component (see Barrouillet, Bernardin, & Camos, 2004 for the attentional focus, Baddeley, 2003 for the central executive and Cowan, 1999 for the focus of attention). Although literature on the relationship between attention and syntax is very scarce, Finney and colleagues demonstrated that the capacity to switch attentional focus predicted the online comprehension of object structures in TD English-speaking children, indicating that the ability to momentarily remove an item from the focus of attention in order to attend to a different item is crucially involved in the processing of complex syntax (Finney, Montgomery, Gillam,

& Evans, 2014). Furthermore, it has been reported that 40-60% of children diagnosed with ADHD have co-occurring language impairments (Cohen, Davine, Horodezky, Lipsett, &

Isaacson, 1993; Oram, Fine, Okamoto, & Tannock, 1999), and that 20-40% of children with

28 While session duration and training frequency of the scholastic training group was matched to that of the WM training group, the scholastic activities focused mainly on the long-term storage of information related to spelling, history, vocabulary etc. In this sense, the scholastic training did not provide the same level of targeted cognitive stimulation as that of Magic Memory. Furthermore, as the scholastic training did not contain activities that required the participants to perform a challenging task within a strict time limit, it was generally less cognitively demanding than the WM training.

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language deficits have co-occurring ADHD (Beitchman, Hood, Rochon, & Peterson, 1989;

Cantwell & Baker, 1991), suggesting there is an important interaction between the evolution of attention and the evolution of language. This interaction has been observed in the DLD population, with Ebert and Kohnert’s (2011) meta-analysis supporting the claim that children with DLD often have attentional difficulties. It is thus conceivable that improved 3p clitic performance in our study was related to an increase in attentional resources which may, on the one hand, allow the DLD participants in the WM training group to become more attentive to the linguistic signals around them in order to pick up on the more subtle, unstressed syllable sequence and integrate it into the prosodic hierarchy and, on the other hand, provide these children with more “fuel” (i.e. a cognitive boost) to complete the high-cognitive-load task of producing this syntactically complex structure. From a theoretical standpoint, highlighting the importance of not only WM resources but also attentional resources to the performance of complex syntactic operations would suggest that the theoretical assumptions of the DCH as put forward by Jakubowicz (2011) only partially describe syntactic development, as computational complexity would be sensitive to cognitive constraints other than WM limitations. In future work, it seems important to include measures of attention in the pre- and post-training test batteries in order to investigate exactly which cognitive ability (WM, attention or both) facilitated or triggered progress in syntax. Furthermore, it seems important to determine which subtype of attention relates to syntax. This would allow clinicians to better orient their intervention, by focusing, for example, on the attentional capacities of children with DLD.

In line with the idea that the Magic Memory training may have facilitated the participants’

ability to attend to the verbal stimuli around them, thus leading to gains in syntax, it is also possible that such training also trains the amount of time it takes to efficiently perform a mental task, i.e. processing speed. Indeed, two of the five Magic Memory activities (Activities 2 and 3) required the participants to perform a mental task (e.g. make a visual comparison of quantity) in a short amount of time. While our study is not designed to measure potential processing speed increases, the possibility that our WM training program trained the rate at which information is processed cannot be ruled out. If the pace at which the children processed information did indeed increase following the WM training regime, it could be supposed that this increase had an ameliorating effect on syntax, similar to the effect reported by Ebert and Kohnert (2009) that training processing speed led to expressive language gains in children with DLD. In what concerns 3p clitics, it could be claimed that faster processing speed enhances one’s ability to process linguistic input before it is subject to decay in WM. Thus, improving

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processing speed would promote the more efficient use of WM, which itself would advance the development of complex syntax, such as 3p clitics. Again, this would suggest that cognitive training is an important complement to more traditional types of intervention.

In conclusion, the results from this study are very promising regarding the potential impact of cognitive training on language abilities. It was shown that the novel WM training program, designed specifically to train verbal WM, leads to improvements in verbal WM on untrained tasks in both children with DLD and in TD children. Additionally, following the WM training regime, there was a measurable increase in the number of 3p clitics produced by children with DLD, a structure known to be problematic for individuals with DLD. This seems to suggest that targeted WM training generalizes to performance on tasks involving different cognitive constructs. Although a direct link between the improvements made in WM and the improvements made in syntax could not be found, we argue that it was specifically the targeted WM training sessions, as opposed to the general cognitive stimulation of the scholastic program, that served as a mental workout, boosting not only the verbal components of the WM system but perhaps sustained attention and processing speed as well. We believe that all three factors – (i) the ability to attend to unstressed, subtle linguistic input, (ii) to simultaneously retain in memory morphosyntactic information about the stimuli and link this information to two different syntactic positions, and (iii) to process this information in a timely manner before it is subject to loss – could be influential for the development of 3p clitics. Thus, it may be the case that the improvements made in syntax are related to possible improvements in sustained attention and/or the rate at which children could process information during a mental task.

Future research should include these measures in order to shed more light on this aspect of the language-cognition interface.

3.4.4 Clinical implications

We have shown that an intervention that focuses on remediating the weak cognitive processing of children with DLD promotes not only stronger WM abilities, but also stronger syntactic abilities and perhaps another mediating component, such as attention or processing speed, which remains to be more clearly elucidated. As such, the logical next step would be to make this training program available to clinicians in order to provide them with innovative material that has been scientifically proven to be beneficial to children with DLD who present dual deficits in WM and syntax. Such tools are still rare even though an evidence-based practice approach, which promotes the consideration of scientific evidence in the clinical

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making process, has been embraced by professionals in disciplines such as psychology and education, and intervention techniques grounded in such principles are preferred in speech therapy (Sackett, Straus, Richardson, Rosenberg, & Haynes, 2000).