The unique orthographic complexities of Japanese, which utilizes multiple types of scripts (morphographic kanji and syllabic hiragana and katakana) for the same spoken language, place unique demands on early learners. Much research has centered on the average ability of Japanese readers, but given the varying challenges of these scripts, attention may need to be oriented towards the outer bounds of ability, specifically those who both deeply struggle (including dyslexia) and excel at reading. In this article, we provide a review of past research on Japanese literacy along with a pre‐registered analysis using quantile generalized additive models that tested two theories in cross‐language literacy research, the orthographic depth and breadth hypotheses. Our results confirmed that the relationships between cognitive skills (phonological awareness and morphological awareness) and reading outcomes differed by script (hiragana vs. kanji). However, their relationships varied in curvilinearity and associations seemed to change based on reading ability. These findings provide supporting evidence for the general scope of the orthographic depth and breadth hypotheses, but may ultimately question the uniformity of these theories.

中文翻译：

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日语读写能力的极限：超越平均阅读的界限

日语独特的拼写复杂性，对同一种口语使用多种类型的文字（形态汉字、音节平假名和片假名），这对早期学习者提出了独特的要求。许多研究都集中在日本读者的平均能力上，但考虑到这些脚本面临的不同挑战，注意力可能需要转向能力的外部界限，特别是那些既深陷阅读困难（包括阅读障碍）又擅长阅读的人。在本文中，我们回顾了过去关于日语读写能力的研究，并使用分位数广义加性模型进行了预先注册的分析，该模型测试了跨语言读写能力研究中的两种理论，即拼写深度和广度假设。我们的结果证实，认知技能（语音意识和形态意识）与阅读结果之间的关系因文字（平假名与汉字）而异。然而，他们的关系在曲线上有所不同，并且关联似乎根据阅读能力而变化。这些发现为拼字法深度和广度假设的一般范围提供了支持证据，但最终可能会质疑这些理论的一致性。