Lexicality and stimulus length effects in Italian dyslexics: role of the overadditivity effect.
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).
Di Filippo
Gloria
G
Neuropsychology Unit, IRCCS Fondazione Santa Lucia, Roma. gloria.difilippo@uniroma1.it
de Luca
Maria
M
Judica
Anna
A
Spinelli
Donatella
D
Zoccolotti
Pierluigi
P
D000328:Adult; D004410:Dyslexia / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007558:Italy; D007802:Language; D008297:Male; D011930:Reaction Time; D014825:Vocabulary