DOI: 10.25442/hku.30071692.v1
title: Supporting data for Distinct Roles of Working Memory Span and Precision in Word Reading and Mathematics Skills in Children with Learning Difficulties

description: The association between working memory and word reading or mathematics skills have been extensively explored. However, the existing evidence has predominantly relied on WM span-based tasks that measure the quantity of items stored in WM, neglecting the quality of stored item representations, i.e., WM precision. This limitation is particularly important in understanding the shared and distinct cognitive mechanisms underlying reading difficulties (RD), mathematics difficulties (MD), and their comorbidity (RDMD). Therefore, using a continuous report paradigm to assess WM precision, this thesis addressed this gap by investigating the distinct roles of WM span and WM precision in word reading and mathematics skills among Chinese third graders, and examined WM precision profiles across learning difficulty subgroups.Study 1 examined the distinct and interactive contributions of WM span and WM precision to Chinese word reading, considering the phonetic regularity and character frequency. Results from a generalized linear mixed model indicated that WM precision was positively correlated with irregular characters reading across children with all WM span levels, whereas such positive association with regular characters reading only observed for those with low WM span. For two-character words, WM precision was positively correlated with word reading, while WM span was only positively correlated with irregular but not regular characters. These findings highlight the importance of WM precision for phonetic irregular characters, especially for those with limited WM span.Study 2 investigated the effects of WM span and WM precision on math facts fluency and word problems, through the interplay with number sense based on the Pathways to Mathematics Model and Hierarchical framework underpinning mathematics skills. After controlling for nonverbal intelligence and language skills, results from structure equation model analyses showed that WM span directly predicted mathematics skills, while WM precision operated indirectly through number line estimation for word problems or conditionally for math facts, interacting with non-symbolic comparison, with stronger positive association in children with high WM precision. This demonstrates that WM precision supports mathematics skills through foundational number sense.Study 3 characterized WM precision profiles across children with RD, MD, comorbid RDMD, and typically achieving peers using continuous report tasks under varying cognitive loads (the number of items to be remembered: set sizes 1-4). Children with RD exhibited comparable WM precision to TA peers. Those with MD showed deficits only under high cognitive load conditions. Critically, the RDMD group demonstrated severe, generalized impairments across all set sizes, with a steeper increase in WM precision errors as cognitive load increased, indicating a fundamental deficit in their WM representational quality.In conclusion, this thesis demonstrated WM precision as a distinct cognitive factor from WM span with unique contributions to academic skills. The findings reveal heterogeneous profiles across learning difficulties, highlighting that comorbidity is not merely additive but may represent a unique phenotype with severe WM precision deficits. These results provide a more nuanced cognitive account of learning difficulties, suggesting that WM precision may serve as a critical diagnostic and intervention target, especially for children with comorbid RDMD.