Different letter-processing strategies in diagnostic subgroups of developmental dyslexia

Abstract

Normally reading adults (N = 15) and primary school children (N = 24) and two diagnostic subgroups of children with developmental dyslexia (N = 21)-all native German speakers-performed a successive same-different task with pairs of letters and nonletters (pseudoletters or geometrical shapes). The first item of a pair was always presented on its own, and the second either on its own or surrounded by a congruent or incongruent nontarget shape. Adults showed congruence effects with nonletters but not with letters, and children with both types of stimuli. Frequent-word reading-impaired dyslexics (N = 11) in addition showed dramatically slower overall reaction times. Nonword reading-impaired dyslexics (N = 10) showed congruence effects with nonletters but negative congruence effects with letters. The results support the notion that normal readers have established a special visual processing strategy for letters. Processing speed rather than reading expertise seems crucial for this strategy to emerge. The contrasting effects between subgroups of dyslexics reveal specific underlying deficits.