Cognitive underpinnings of multidimensional Japanese literacy and its impact on higher-level language skills.

This study aimed to identify the cognitive underpinnings of Japanese kanji abilities and clarify the contributions of kanji acquisition to the development of higher-level language skills based on a three-dimensional view of kanji abilities encompassing reading accuracy, writing accuracy, and semantic comprehension. First, a series of regression analyses was used to identify the multifactorial models of each dimension of Japanese kanji acquisition. These models suggest that, among basic cognitive skills, naming speed, visuospatial processing, and syntactic processing underpin kanji abilities in a dimension-specific manner, whereas phonological processing is a common factor. Second, although all the dimensions of kanji abilities predicted acquired verbal knowledge equally, writing skills on the text level, measured as idea density, were only predicted by the writing dimension (indirectly via acquired knowledge). Our findings represent the first evidence of the dimension-specific relationships of the three dimensions of Japanese kanji abilities with their cognitive predictors, as well as with higher-level language skills. They suggest the importance of handwriting acquisition during school years for the development of language skills through to adulthood. Finally, taking the seminal "Nun study," which suggests that higher idea density is protective against dementia, into account, we propose a theoretical framework for the lifelong trajectory of literacy acquisition.