| Few studies have examined whether inhibition impairments in Attention Deficit/Hyperactivity Disorder (ADHD)---well-established in the motor output domain---extend to higher-order cognition such as language processing. This study explored whether inhibitory mechanisms that protect language comprehension are impaired in ADHD, and whether such inhibitory deficits, if they exist, clarify the etiology of the high rate of co-occurrence between ADHD and Reading Disorder (RD). Two language comprehension tasks from the cognitive literature believed to probe inhibitory mechanisms were used: (1) a sentence-level lexical ambiguity meaning judgment task that measured interference control, and (2) a syntactic garden path revision task which examined ability to use semantic cues to revise misinterpretations "on-line" during sentence comprehension.; 97 children aged 7 to 14 with ADHD or RD participated in the study after thorough diagnostic assessment with structured diagnostic interview and parent and teacher ratings. Both (a) higher levels of inattention and (b) ADHD diagnosis were associated with poorer inhibitory control of irrelevant information during lexical ambiguity resolution (e.g., r = .26, p < .05), as well as with decreased ability to revise or suppress misinterpretations after syntactic garden paths (e.g., r = .32, p < .01). Girls with ADHD were more impaired than boys (interaction: p < .01). For children with RD, lower-order language problems (e.g., word decoding, understanding complex syntax) affected higher-order inhibitory processes during language comprehension, yielding findings similar to those found in children with ADHD. Taken together, the pattern of results suggested that ADHD and RD do share deficits in inhibitory mechanisms that protect higher-order language comprehension, but that these may develop via different pathways. In ADHD, these impairments may develop directly from core cognitive inhibition deficits, whereas in RD they may arise secondarily to language automatization failures and subsequent requirements for more effortful processing of language (which leaves fewer resources for inhibition in higher-level language tasks). This was the first study to use these tasks to assess inhibitory mechanisms in language comprehension in ADHD. Identification of these difficulties may help clarify the role of language in the self-regulatory and executive functioning problems that characterize the disorder. Implications for understanding the etiology of the high co-occurrence of ADHD and RD are discussed. |
