Litt, R. & Nation, K.
University of Oxford
Children with dyslexia exhibit specific deficits in visual-verbal paired associate learning (PAL) that cannot be explained by general associative learning deficits (e.g. Vellutino, Steger, Harding, & Phillips, 1975).These deficits are observed across languages, despite variations in orthographic, phonological, and morphological complexity (Li, Shu, McBride-Chang, Liu, & Xue, 2009; Mayringer & Wimmer, 2000; Messbauer & de Jong, 2003). However, whether these deficits reflect difficulties in crossmodal mapping or verbal learning is less clear. We present a series of experiments investigating this question. Experiment 1 investigated the specificity of PAL deficits by dissociating crossmodal and verbal demands. Children with dyslexia (N = 18) and age-matched controls (N = 18) were compared across the following mapping conditions: visual-verbal, verbal-verbal, visual-visual, and verbal-visual PAL. One mapping condition was tested per week for four weeks. Participants completed a computerized PAL task comprised of two presentation blocks and five test blocks with feedback. Accuracy across trials was analyzed in a logistic linear mixed effects model. Experiment 2 investigated whether visual-verbal PAL deficits reflect difficulties in the verbal learning or associative learning component of the task. Children with dyslexia (N = 14) and age-matched controls (N = 14) were tested across two days. On day one, children were pre-exposed to the phonological forms in a nonword learning task. On day two, children learned to pair the same nonwords with visual forms. Performance was analyzed in a linear mixed effects model. Children with dyslexia exhibited selective deficits in visual-verbal and verbal-verbal PAL, but performed as well as their peers in verbal-visual and visual-visual PAL. Results of Experiment 2 revealed an item-specific relationship between nonword learning and later associative learning success. Additionally, associative learning deficits were fully accounted for by verbal learning deficits. There was no evidence for an additive relationship between the two.