The Efficacy of Explicit vs. Implicit Intervention Procedures for Cantonese Children With Developmental Language Disorder: A Randomized Controlled Trial

This project is the first to adopt a randomized controlled trial (RCT) to compare the efficacy of explicit vs. implicit intervention on relative clause production (subject relative clause in object position of the main clause or SRC-O) in Cantonese-speaking children with DLD and to use an individual difference approach to identify predictors of intervention outcomes.

The investigators aim to examine the following three specific questions:

1. Will the explicit intervention (Shape Coding+syntactic priming) on relative clause production lead to better outcomes than implicit intervention (syntactic priming only)? Based on the Procedural circuit Deficit Hypothesis (PDH), the investigators hypothesize that explicit intervention would switch the reliance of learning to the relatively intact declarative learning circuitry and lead to better outcomes than implicit intervention.
2. Can pre-intervention procedural learning, working memory (WM) capacities, and grammar impairment severity predict the intervention outcomes across children with DLD? Based on the PDH, the investigators hypothesize that children with lower procedural learning abilities will demonstrate worse outcomes in the implicit intervention group, but better outcomes in the explicit intervention group. As for WM and grammar impairment, the investigators hypothesize that children with better WM or grammatical abilities will demonstrate better outcomes in both groups.
3. Will 10 intervention sessions (500 doses of the target structure) lead to learning progress in children with DLD, even with implicit intervention, and will the progress plateau at some point of the intervention? As informed by previous studies, the investigators hypothesize that more exposure to the target structure, especially with high variability in the input, will lead to improvement, even for the implicit intervention group. The investigators will explore whether the progress will plateau over the course of interventions and compare the learning trajectory between explicit and implicit interventions.

A total of 32 Cantonese-speaking school-age children with DLD (5-8 years old) will be recruited (N=16/group). The children will be pre-screened with an online questionnaire on language background and case history, and then assessed on the Raven's Standard Progressive Matrices (~25 min), hearing screening (~5 min) and Hong Kong Cantonese Oral Language Assessment Scale (HKCOLAS) (~90 min) to confirm DLD. Eligible children will be assigned to one of the two intervention groups following a random allocation sequence of letters "A" and "B" (e.g., ABBBA...), where A and B refer to the explicit and implicit intervention respectively, on a 1:1 allocation ratio.

The study consists of pre-intervention assessments and an intervention phase. For pre-intervention assessments, children's procedural learning, declarative learning, and working memory capacities will be assessed using the serial reaction time (SRT) task, old/new picture recognition task, and forward and backward digit span test, respectively. The purpose is to examine the predictive power of these capacities in the individual children's intervention outcomes.