Executive functioning in adults and children with developmental dyslexia.
The performance of developmentally dyslexic children and adults was studied upon a range of tasks that involved executive functioning. Both adult and child samples of dyslexics were found to under-perform on the group-embedded figures test. This test required the identification of constituent parts from within complex visual arrays, with good performance necessitating the inhibition of the processing of the surrounding context. A general deficit on visual-spatial tasks was eliminated as an explanation as dyslexics performed normally upon a range of other non-verbal assessments. The dyslexics consistently demonstrated a deficit in digit span tasks, a decrement that was increased with distractors, again suggesting difficulties in inhibiting the processing of the surrounding context. A deficit was also identified upon a verbal fluency task without a deficit in vocabulary level. Additionally, a specific deficit in the recollection of the temporal order of the presentation of items was in evidence, without a deficit in the recognition of the items themselves. The findings taken as a whole suggest that dyslexic individuals show deficiencies in executive functions relating to inhibition of distractors and to sequencing of events, a set of tasks associated with left prefrontal cortex functioning in the acquired neuropsychology literature.