This study evaluated letter recognition processing in Italian developmental dyslexics and its potential contribution to word reading. Letter/bigram recognition (naming and matching) and reading of words and non-words were examined. A group of developmental dyslexics and a chronologically age-matched group of skilled readers were examined. Dyslexics were significantly slower than skilled readers in all tasks. The Rate and Amount Model (RAM, Faust et al., 1999) was used to detect global and specific factors in the performance differences controlling for the presence of over-additivity effects. Two global factors emerged. One (letter-string factor) accounted for the performance in all (and only) word and non-word reading conditions, indicating a large impairment in dyslexics (more than 100% RT increase as compared to skilled readers). All the letter/bigram tasks clustered on a separate factor (letter factor) indicating a mild impairment (ca. 20% RT increase as compared to skilled readers). After controlling for global factor influences by the use of the z-score transformation, specific effects were detected for the letter-string (but not the letter) factor. Stimulus length exerted a specific effect on dyslexics performance, with dyslexics being more affected by longer stimuli; furthermore, dyslexics showed a stronger impairment for reading words than non-words. Individual differences in the letter and letter-string factors were uncorrelated, pointing to the independence of the impairments. The putative mechanisms underlying the two global factors and their possible relationship to developmental dyslexia are discussed.
Letter and Letter-String Processing in Developmental Dyslexia
Tipografica Varese., Varese, Italia
Cortex (Testo stamp.) 46 (2010): 1272–1283.
info:cnr-pdr/source/autori:De Luca, M., Burani, C., Paizi, D., Spinelli, D., & Zoccolotti, P./titolo:Letter and Letter-String Processing in Developmental Dyslexia/doi:/rivista:Cortex (Testo stamp.)/anno:2010/pagina_da:1272/pagina_a:1283/intervallo_pagine