Visual processing of verbal and non-verbal stimuli in reading disabilities

This study was designed to investigate whether learning disabled children are slower at processing visual information in general (compared to children of comparable age and reading level), or if their deficit is specific to the written word. Computerized backward masking and temporal integration tasks were used to assess the speed of visual information processing. Stimulus complexity (simple, complex) and type (verbal, non-verbal) were varied creating a 2x2 matrix of stimulus conditions: simple non-verbal, complex non-verbal, simple verbal and complex verbal. Reading disabled (RD) adolescents demonstrated difficulties in processing rapidly presented verbal and non-verbal visual stimuli. although the effect was magnified when processing verbal stimuli. Thus, the results of this study suggest that some reading disabled youths have visual temporal processing deficits that compound difficulties in processing verbal information during reading. A high proportion of the reading disabled adolescents were also diagnosed with attention deficit hyperactiviey disorder (ADHD). Adolescents with co-morbid ADHD and RD demonstrated similar overall deficits, demonstrating poorer performance for complex stimuli than the RD group in the backward masking task. However, the RD/ADHD group were actually more efficient than the RD group in complex conditions in the temporal integration task - a finding that needs to be replicated and explored further.