Serial mechanism in transposed letters effects: A developmental study

- Transposed letter (TL) effects reflect the orthographic processing in reading.
- Young children and adults show TL effects in lexical decision.
- Tl effects increase with age in reaction times.
- TL effects are larger in final than initial position.
- Serial position effect reflects interaction of lexical and sublexical mechanisms.

The study describes the developmental trend of transposed letters (TL) effects in a lexical decision task. The TL effect refers to the fact that nonwords derived from words by transposing two middle letters (e.g., talbe from table) are responded to more slowly than control nonwords in which two letters are replaced (RL [replaced letters]; e.g., tafde). We measured this effect in three groups of children (second, third, and fifth graders) and a group of adults. Length was manipulated with short letter strings (four or five letters) and long letter strings (seven or eight letters). In long letter strings, position of letter transposition/replacement was also manipulated; half of the stimuli contained the TL/RL toward the beginning of the string and half toward the end of the string. The results showed that the size of the TL effect increased with age and that this developmental pattern was more marked for transpositions involving the final part of the word. The results suggest that with the increase in reading ability, the reading system relies more strongly on a coarse orthographic representation in which letter position is not precisely coded. Furthermore, the effect of position suggests that a serial mechanism is used to scan the letter string. This determines the extent to which nonwords activate the base words, modulating the influence of lexical effects in nonword decisions. The nature of this effect is discussed.