Lexicality and stimulus length effects in Italian dyslexics: Role of the overadditivity effect

Gloria Di Filippo, Maria De Luca, Anna Judica, Donatella Spinelli, Pierluigi Zoccolotti

Research output: Contribution to journalArticlepeer-review


The effect of lexicality and stimulus length was studied in 32 third- and fourth-grade Italian dyslexics and in 86 age-matched controls. A visual lexical decision task was used. As proposed by Faust et al. (1999), the results were analyzed in terms of raw reaction time (RT) data and using the z-score transformation to control for the presence of overadditivity effects. In terms of RTs, dyslexics showed a larger difference between words and nonwords (lexicality effect) and between short and long stimuli (length effect) than proficient readers. When data were transformed into z scores, only the group by length interaction remained significant while that with lexicality vanished. This pattern indicates that stimulus length has a specific role in Italian dyslexics' reading deficit; in contrast, slowness in responding to nonwords was not specific but was interpreted as one aspect of dyslexics' general inability to deal with alphabetical material (overadditivity effect).

Original languageEnglish
Pages (from-to)141-149
Number of pages9
JournalChild Neuropsychology
Issue number2
Publication statusPublished - May 2006


  • Italian
  • Length
  • Lexical decision
  • Lexicality
  • Reading
  • Shallow orthography

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Neuropsychology and Physiological Psychology


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