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This research examines the acquisition of letter-position processing. Study 1 investigated letter-position processing in Grades 1-6 and adult readers, using the occurrence of specific error types as the outcome measure. Between Grades 1 and 2, there was a shift from making more other-word to making more letter-position errors. This shift was a function of reading proficiency, not of years of reading instruction. Based on the multiple-route model of reading development (Grainger, Lété, Bertand, Dufau, & Ziegler, 2012), we argue that the fact that children make fewer other-word errors (i.e., mostly letter-identity errors) opens up the opportunity for them to make "the more advanced" letter-position errors. Finally, skilled adult readers still made fewer letter-position errors than typical readers in Grade 6, suggesting that the acquisition process is not finalized by the end of primary school. In Study 2, we directly compared letter-position processing with letter-identity processing. Thirty children in Grade 3 and 30 children in Grade 4 read aloud words with and without higher-frequency distractors. Children more often misread a word with a higher-frequency distractor than without such a distractor and this effect was stronger for below-average than for above-average readers. Converging with the results of Study 1, we found that a letter-position distractor is more disruptive than a letter-identity distractor. These results confirm that the acquisition of letter-position processing lags behind of that of letter-identity processing. The results are discussed within the framework of the Lexical Tuning Hypothesis (Castles, Davis, Cavalot, & Forster, 2007), which stresses the importance of feedback between letter (identity and position) coding and (developing) orthographic representations.

Masked transposed-letter (TL) priming effects have been used to index letter position processing over the course of reading development. Whereas some studies have reported an increase in TL priming over development, others have reported a decrease. These findings have led to the development of 2 somewhat contradictory accounts of letter position development: the lexical tuning hypothesis and the multiple-route model. One factor that may be contributing to these discrepancies is the use of baseline primes that substitute letters in the target word, which may confound the effect of changes in letter position processing over development with those of letter identity. The present study included an identity prime (e.g., listen--LISTEN), in addition to the standard two-substituted-letter (2SL; e.g., lidfen--LISTEN) and all-letter-different (ALD; e.g., rodfup--LISTEN) baselines, to remove the potential confound between letter position and letter identity information in determining the effect of the TL prime. Priming effects were measured in a lexical decision task administered to children aged 7-12 and a group of university students. Using inverse transformed response times, targets preceded by a TL prime were responded to significantly faster than those preceded by 2SL and ALD primes, and priming remained stable across development. In contrast, targets preceded by a TL prime were responded to significantly slower than those preceded by an ID prime, and this reaction-time cost increased significantly over development, with adults showing the largest cost. These findings are consistent with a lexical tuning account of letter position development, and are inconsistent with the multiple-route model.