Individual differences and grade-related changes in sensitivity to the statistical structure of word forms in a shallow writing system

The present study investigates a principal mechanism underlying reading development and individual differences in reading skills, namely sensitivity to orthotactic regularities in lexical processing. This sensitivity can be seen as a reflection of statistical learning (SL), as it pertains to accumulated experience with statistical regularities in print. However, empirical evidence regarding the link between such sensitivity and reading skills remains mixed, and it is particularly unclear what role it plays in orthographically shallow languages. The present study addressed this issue by assessing sensitivity to orthotactic regularities in Finnish pseudowords using a lexical decision task, and examining how this sensitivity depends on vocabulary skill and grade by comparing students from grades 3, 4, and 7 ( N = 818). We identified distinct differences between grade levels, with the orthotactic sensitivity effect being significantly stronger in higher grade levels. Furthermore, we observed substantial within-grade individual differences, with higher vocabulary proficiency predicting greater effects of orthotactic regularities in pseudowords. These findings demonstrate a link between sensitivity to orthotactic constraints and linguistic skills. Importantly, our findings indicate that sensitivity to statistical information is critical even in markedly shallow orthographies, challenging earlier literature. We discuss the implications of our findings for SL views of reading. We also discuss whether sensitivity to regularity exists at the level of orthotactics, phonotactics, or both, given that in the shallow writing system of Finnish the distinction between these levels is blurred.