Abstract: Reading Disability (RD) and Attention-Deficit/Hyperactivity Disorder (ADHD) are two of the most common disorders of childhood, which are often co-morbid with a rate from 25% to 40% nationally. It is widely accepted that the proximal cognitive cause of RD is a phonological deficit whereas the predominant account of ADHD sees it as a result of an impairment in executive functions that affect both cognitive and motivational systems. The co-occurrence raises questions as to how the disorders interact and in which respect (also to what extent) they can be differentiated. However, studies of either disorder alone cannot test definitively whether RD and ADHD are separable at the cognitive level, because individuals with each disorder might also be significantly impaired on measures of the core deficit associated with the other diagnosis. In addition, an increase of homogeneity across groups and use of mutually exclusive definitions for group assignment are recommended, and the differences in the tasks of cognitive function that are utilized might account for heterogeneity of performance of children with RD or ADHD. Therefore, few studies have shown a fairly clear distinction between core deficits in this two disorders. This study tested a double dissociation between Chinese children with RD and ADHD on measures of basic language processing and inhibition in order to compare the core cognitive deficits in these two disorders. All of the disorder participants were recruited at a clinic and normal children were recruited from an elementary school. Four groups of children, carefully diagnosed by clinicians, aged between 7 and 12 years (15 RD-only, 17 ADHD-only, 19 RD + ADHD, 18 typically developing normal controls), were assessed on measures of basic language processing, response inhibition and higher-level language processing. Three tests, including phonological awareness test, rapid naming test and morphological awareness test were used to assess the ability of basic language processing among these groups. The classic Stop Signal task was used to assess the response inhibition of subjects in different groups. At last, the Sentence Span task was used to assess the higher-level language processing, namely the verbal working memory of subjects, which contains and synthesizes the phonological processing ability and interference suppression ability. The results indicated that both RD-only group and RD + ADHD group performed significantly worse than the ADHD-only group and NC (normal controls) group on the measures of phonological awareness, rapid naming and morphological awareness, but no significant differences had been detected between ADHD-only group and NC group. With regard to the response inhibition, the ADHD-only group and RD + ADHD group performed significantly worse than the RD-only group and NC group on the stop signal task, and there was no significant differences between the RD-only group and NC group. All the three disorder groups (RD-only, ADHD-only, RD + ADHD) performed significantly worse than the NC group on the Sentence Span task, and no significant differences were found among the three disorder groups. These findings suggest that RD is associated independently with weaknesses in the basic language processing, including the phonological awareness, rapid naming speed and morphological awareness, whereas ADHD was independently associated with a weakness in inhibitory control. That is, the core cognitive deficits of Reading Disability and Attention-Deficit/Hyperactivity Disorder are independent from each other.

Key words: Reading Disability, ADHD, language processing, response inhibition, cognitive deficits

摘要： 阅读障碍与注意缺陷多动障碍(ADHD)高度共病，以往研究结果显示两种障碍在语言加工、执行功能等领域的缺陷既相似又不同。本研究采用语音意识测验、快速命名测验、语素意识测验和停止信号任务，以及阅读广度测验，分别考察四组被试（阅读障碍组、ADHD组、双重障碍组、正常控制组）的基础语言加工、反应抑制和言语工作记忆能力，结果发现：阅读障碍组和双重障碍组在语言加工任务上的成绩均显著差于ADHD组和正常组；ADHD组和双重障碍组在停止信号任务上的成绩显著差于阅读障碍组和正常组；所有障碍组在阅读广度测验上的成绩显著差于正常组。表明阅读障碍的特异性缺陷体现在语言加工过程上，而注意缺陷多动障碍的特异性缺陷体现在反应抑制上。这对于今后单一障碍的研究及临床诊断和干预具有重要的参考价值。

关键词: 阅读障碍, ADHD, 语言加工, 反应抑制, 认知缺陷