苏州大学本科生毕业论文
同起来. 然而,事实上WM与短时记忆的区分是WM研究中的一个基本问题. 现在比较一致的观点是,二者在功能上存在显著差异但在结构上是类似的. 从功能上看,WM 是指被暂时贮存的内容在之后的复杂认知活动中是必不可少的,是进行其他认知活动的前提基础,如心算中的暂时储存;短时记忆则是指所储存的信息在之后的认知加工中指望使用的记忆机能,如只要拨出去就可能忘掉的电话号码的暂时贮存,焦点侧重于信息的保持. 从结构上看,二者的区分要复杂些,大多数研究者认为WM系统包含短时记忆 ,也就是说,WM系统是由“短时记忆”和“执行功能”构成的。 但是这里说的短时记忆是指短时贮存,而光有这种短时储存库是不能实现短时贮存机能的. 因为,双重贮存模型指出,为了实现短时记忆机能,除了短时贮存库,还需要执行机能的参与. 因此,从这观点来看,短时记忆系统和WM系统都是由短时贮存和执行机能构成的,二者在系统组成上没什么差别. 因此,WM 和短时记忆的差异在于系统的工作方式不同,前者比后者需要更多的执行功能参与,不仅支持保持功能,而且用于支持认知活动中的动态记忆,承担着更复杂的认知任务.从上述分析可以看出,WM比短时记忆的功能更多、含盖范围更广. WM能包含短时记忆,而短时记忆则代表不了WM.
众所周知,WM的容量是有限的. 那么,WM 容量为什么有限? 受什么因素制约呢? 这是WM研究中的根本问题之一. 人们从多种角度对此问题进行了探讨. Towse 等认为信息在时间上的衰退可能是限制WM广度的主要因素. 如被试在信息保持上所花的时间越长,容易遗忘的目标信息也越多. 该观点与传统的衰退说有相似之处. Lustig 等人则认为WM 广度的决定因素是对来自先前试验的前摄干扰的感受性,对抗干扰能力相同的被试而言,WM广度成绩随影响前摄干扰量的变化而变化. Engle 等则发现WM 广度由短时记忆容量和注意控制功能的效率共同决定。Oberauer 则认为,WM容量实际反映了可同时直接提取的项目数. 其资源限制主要受两种因素制约:一是WM表征的覆盖(overwriting) ,即共享特征的记忆表征在特征编码上相互混淆;二是某个项目被提取时所产生的不同项目间的干扰和竞争. Lustig认为记忆广度测验不仅包括了处理当前信息的能力,还需要对先前的信息进行成功的管理,具有较大记忆广度的个体善于应对测验任务的系列项目之间的影响即前摄抑制。Engle甚至声称工作记忆就是处理前摄抑制的系统。n2back 任务涉及了工作记忆中央执行的重要机制,即对记忆集的更新操作,是根据新呈现的信息,对工作记忆中的内容进行持续修正的能力。需要将暂时不需要的项目排除在工作记忆之外,对工作记忆项目进行重新排序,在工作记忆中增加新的项目。前摄抑制是对工作记忆中无关信息(即来自之前旧的项目) 的积极抑制过程,耗费认知资源。先前项目与最近项目相似程度越大,抑制它的难度越大。本研究中,在最近负探测下,无关项目并非目标,却与探测项目完全相同,所带来的干
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苏州大学本科生毕业论文
扰要比Kiss研究中由于序列长度所产生的干扰效应大,耗费认知资源更多,抑制冲动反应难度更大。本研究中,将测查前摄抑制的任务范式和记忆更新n2back 任务范式结合在一起,考察了被试在前摄抑制12back 任务中的表现。被试在对探测刺激和第n 个项目的靶刺激进行匹配时有可能受到了来自前面无关项目的干扰,最近负探测和非最近负探测条件下成绩的差异反映了前摄抑制对任务的影响。结果发现ADHD 儿童受到前摄抑制的影响成绩大幅下滑,ADHD 伴随阅读障碍儿童的成绩也大幅下滑,程度与ADHD 组一致。阅读障碍儿童和正常控制组儿童的成绩也有下降,两者差异并不明显,这说明前摄抑制是影响工作记忆容量的重要因素,并且ADHD 儿童更加容易受到前摄抑制的影响,这是导致其工作记忆成绩缺损的重要原因,而阅读障碍儿童能够像正常儿童一样,在一定程度上处理前摄抑制,前摄抑制对正常儿童工作记忆的影响效应量在15 %左右,但是对ADHD 的影响要高得多(25 %以上).受前摄抑制的影响,正常被试和障碍被试的前摄抑制12back 任务成绩均明显下滑,说明前摄抑制是影响工作记忆容量的一个重要因素。前摄抑制对ADHD 儿童、阅读障碍儿童和正常儿童的言语工作记忆成绩的影响程度不同。ADHD 和ADHD 伴随阅读障碍儿童成绩大幅下滑(26144 % ,28144 %) ,程度明显高于正常儿童和阅读障碍儿童(14162 % , 15184 %) , 后两者差异并不明显,这说明了ADHD 儿童言语工作记忆更容易受到前摄抑制的不利影响。
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苏州大学本科生毕业论文
Spatial working memory and strategy formation in adults diagnosed with attention deficit hyperactivity disorder
1. Introduction
Working memory is defined as a cognitive system that provides temporary storage and manipulation of the information necessary for activities such as reasoning, language comprehension and learning (Baddeley, 1992). This process requires the ability to hold information ‘‘on-line’’ during a brief time until a decision and subsequent response is made (Goldman-Rakic, 1990). It has been postulated that there is a dissociation between basic memorial requirements of tasks and their executive components which control response selection, e.g. the adoption of an overall strategy or plan, or the utilization of specific attentional inhibitory mechanisms. Thus performance is determined by two factors, one related to short-term spatial memory and the other to strategic factors (Robbins, 1996). Several studies have shown that spatial working memory deficits in patients with frontal lobe excisions may be related to the inefficient use of a particular search strategy (Miotto, Bullock, Polkey, & Morris, 1996; Owen, Downes, Sahakian, Polkey, & Robbins,1990; Owen, Morris, Sahakian, Polkey, & Robbins, 1996). This suggests that part of the deficit may arise from executive failure and use of a strategy can reduce the load on memory caused by interference from previous choices.
Spatial working memory deficits have been found in studies comparing ADHD and normal children (Karatekin & Asarnow, 1998; Gorenstein, Mammato, & Sandy, 1989; Shue & Douglas,1992). However, most studies have not
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苏州大学本科生毕业论文
considered whether deficits in spatial working memory may be accounted for by problems with strategy formation. The importance of strategy has been considered in other neurological or psychiatric disorders. For example, strategy formation impairment has been shown to be linked to spatial working memory impairment patients with frontal excisions (Miotto et al., 1996) but not for patients with Aspergers Syndrome (Morriset al., 1999).
The current study explores spatial working memory deficits and strategy impairment of ADHD adults using the computerised Executive Golf task (cf. Feigenbaum, Polkey, & Morris, 1996), a development of the spatial working memory task designed by Morris et al. (1988). Working memory is of relevance in the investigation of adult ADHD because it is thought to be particularly impaired in relation to other types of psychiatric disorders that have associated neuropsychological deficits (Gallagher & Blader, 2001). This has been explored in a previous study by Dowson et al. (2004) using a different task but a similar methodology. In the Dowson et al. (2004) study the CANTAB method of measuring spatial working memory involves an array of spatial locations on a screen in which the participant has to avoid going back to previously successful locations.They found impairments on return errors and associated poor strategy when conducting the tasks. The Executive Golf task is more akin to a real life activity in that, as well measuring spatial working memory it simulates a ‘game of golf’, the participant searching for places in which a ‘golfer’is predicted to putt a ball, avoiding returning to these places during subsequent searches. The golf holes are presented using three dimensional computer graphics with the ‘golfer’
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