关键词: 注意缺陷多动障碍, 工作记忆负荷, 新异分心刺激

Abstract: One of the behavioral manifestations of children with Attention Deficit Hyperactivity Disorder (ADHD) is their abnormal apparent distractibility. But a number of attempts to prove that children with ADHD are abnormally distractible have been unsuccessful. Selective or focused attention tasks often do not differentiate children with ADHD from normal controls. One of the reasons may be that most distraction or selective attention tasks are not ecologically valid measures of distraction in daily life situations, because in daily life, the distraction that has to be inhibited is outside the task and not conflicting with task demands. Therefore, some researchers began to explore the mechanism of involuntary attention and distractibility in ADHD, as indicated by cross-modal oddball task. There are a few studies in this field, but the results are opposite. There is a disputation about the effect of novel distracters on children with ADHD. The former suggests that novel distracters can enhance their performance temporarily, while the latter claims that it can enhance distractibility. By analyzing the two viewpoints, the authors have found that the primary reason leading to the disputation of the two viewpoints might be caused by the different working memory (WM) load of the tasks in their experiments. Therefore, the authors speculated that the level of WM load of tasks may have effect on filtering novel distracters in children with ADHD. Besides, the authors speculated that the time interval between distracters and tasks may also have influence on filtering distracters. Previous studies on the ability of filtering novel distracters in children with ADHD have little ecological validity due to the lacking of novelty in choosing distracters; and the debate on the relation between working memory load and filtering distracters always exists. Conducting the task of audio-visual cross-modal oddball, the study aimed at discussing the effect of different working memory load on filtering novel distracters in children with ADHD by operating the level of visual task working memory load and the time intervals between distracting stimuli and target stimuli. 32 ADHD and 35 mental normal children were recruited from a clinic and a normal elementary school respectively. The cross-modal oddball task was administered, comparing filtering distracters ability between ADHD and mentally normal children in different WM load. In this paradigm, the children performed a visual task while listening to standard tones and occasionally a novel environmental sound, such as an engine or a bell. Novel and unexpected stimuli are hard to ignore and cause distraction. There were two tasks. One was low level of WM load, which asked children to judge if two numbers on screen was the same. The other was high level of WM load, which asked children to add two numbers on screen and then judge if the answer given was correct. The results showed that：(1) The ability of filtering distracters in ADHD children depended on the level of WM load. Due to the difference of working memory load, the effect mode was separate. When the level of WM load was low, novel distracters had arousing effect on both groups of ADHD children and normal children. When the level of WM load was high, distracting stimuli had effect on the task process of children in both groups. However, the effect was larger in ADHD children, which suggested their ability of filtering distracters were lower. (2) When distractors and target task were showed at the same time, ADHD children were distracted; but the results were not showed that longer extension of time intervals between target task and distracting task could reduce the interference of novel distracters. It suggested that the extension of time might help ADHD children to reduce distraction, but the arousal state should be considered. Longer extension of time could reduce the state of arousal of ADHD children.