Beyond decoding deficit: inhibitory effect of positional syllable frequency in dyslexic Spanish children

This study explores whether activation and inhibition word processes contribute to the characteristic speed deficits found in transparent orthographies (Wimmer, Appl Psycholinguist 14:1-33, 1993). A second and fourth grade sample of normal school readers and dyslexic school readers participated in a lexical decision task. Words were manipulated according to two factors: word frequency (high vs. low) and syllable frequency (high vs. low). It has been repeatedly found that words with high-frequency syllables require extra time for deactivating the lexical syllabic neighbors: the so-called inhibitory effect of positional frequency syllable (Carreiras et al., J Mem Lang 32:766-780, 1993). We hypothesized that dyslexic readers would show a stronger inhibitory effect than normal readers because they are slower decoders and they may also be slower at the activation and inhibition of word representations that are competing (i.e., syllabic candidates). Results indicated an interaction between word and syllable frequency (i.e., a strong inhibitory effect was found in the low-frequency word condition). According to our hypothesis, the inhibitory effect size was almost three times bigger in dyslexics than in the normal readers. This difference shows an alteration, not a developmental lag. Interestingly, the inhibitory effect size did not interact with school grade. Thus, reading experience did not impact the lexical processes involved on the inhibitory effect. Our outcomes showed how activation and/or inhibition of lexical processes can contribute to the lack of speed beyond decoding deficit.