Speech discrimination and phonological working memory in children with ADHD

This study examined phonological working memory and speech discrimination among children with attention-deficit-hyperactivity disorder (ADHD) with and without motor problems. Forty-one children were assigned to three groups; children with ADHD (N=9), children with ADHD plus developmental coordination disorder (ADHD+, N=13), and age-matched control children (N=19). The subjects' ability to classify stimulus pairs was examined in two experiments. The first experiment required subjects to discriminate pairs of monosyllabic stimuli with contrasting consonants to test speech discrimination without using a working-memory load. In the second protocol, subjects were exposed to two- to five-syllabic non-word pairs with contrasting vowels in order to test speech discrimination with a working-memory load. The subjects classified the pairs as being either the same or different in both experiments. No significant differences were found between the subject groups in the discrimination task with monosyllables. When exposed to the two- to five-syllabic stimuli, the ADHD+ group scored significantly lower than both other groups. This was attributed to a higher sensitivity to working-memory load. Some possible explanations of this effect are discussed.