Different time course of negative priming in the subtypes of ADHD
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The nature of inattention in attention deficit hyperactivity disorder (ADHD) and the issue of whether the inattentive ADHD type (ADHD/IA) represents a true subtype or a distinct condition still remain controversial in ADHD research. According to Barkley’s theory of ADHD (1997), the combined ADHD type (ADHD/C) has deficits in behavioral rather than cognitive inhibition and inattentive symptoms in this subtype are secondary to behavioral inhibition. In contrast, he suggested the core deficit in the ADHD/IA type relates to selective attention, which is separate from behavioral inhibition. Studies of subtype differences in ADHD failed to differentiate the ADHD/IA type from the ADHD/C type although both subtypes were distinct from non-diagnosed controls. In this study, the time course of negative priming and facilitation was tracked using a letter- vii matching and a localization task in order to investigate whether the ADHD/C and ADHD/IA subtypes would show different profiles of selective attention. College students with ADHD/C (n = 10 for the letter-matching task; n = 11 for the localization task), or ADHD/IA (n = 9 for both tasks), and the non-diagnosed controls (n = 14 for the letter-matching task; n =16 for the localization task) performed on two tasks with response-to-stimulus intervals (RSIs) of 500ms and 1000ms. Results indicated that the two ADHD subtypes had different profiles of negative priming on the lettermatching task, but they had similar facilitation profiles on both tasks. The study also addressed problems with negative priming studies in ADHD.