Design

A double-blind, paired designed study.

Time and setting

The training was conducted at one primary school in Wuhan, Hubei Province, China from May to June in 2011. Data collection and analysis were performed from January to September in 2011.

Subjects

The participants were third- or fifth-graders (aged 8–11 years) from one primary school in Wuhan, China. This primary school is located in an urban community of average-level socioeconomic status in Wuhan, China.

Diagnosis criteria

All the dyslexic children were diagnosed according to criterions defined by the International Statistical Classification of Diseases and Related Health Problems (Tenth Revision, ICD-10), issued by World Health Organization^[25].

Inclusion criteria       

Several inclusion criteria were used to ensure that all participants: (1) Vocabulary test scores were at least 1.5 standard deviations lower than children in the same grade, as assessed by the Character Recognition Measure and Assessment Scale for Primary School Children^[26]. (2) The score on the Dyslexia Checklist for Chinese Children was 2 standard deviations higher than the mean score^[27]. (3) The children had normal nonverbal Raven intelligence quotients (intelligence quotient ≥ 85). (4) The children were physically healthy and had no history of neurological disease, head injuries, or psychiatric disorders. (5) Informed consent was obtained from each subject and their parents before initiating testing.

Methods

Procedure

During the week prior to the onset of training, the participants completed a set of assessments in working memory performance and reading achievement. Reading-related skills in the control group were measured within the same time interval as the treatment group. The format of the training was customized for each individual. All children completed two sessions of assessments within the same time intervals: (1) pre-test (T1), (2) post-test 5–6 weeks (T2).

The children in the treatment group engaged in training on a variety of working memory tasks using a computerized game environment. This training was conducted for approximately 40 minutes a day in the school over a period of 5 weeks. Children completed 100–150 trials every day. The time to complete each trial was reduced by 10% when the accuracy of the child in the treatment group increased by one fifth in each task. At the end of each day of exercises, children were allowed to choose a small tangible reinforcement from items such as sports or action figure cards, colored pencils, or a cartoon exercise book. Consistent with Torkel Klingberg’s experimental design^[11], the control group was trained with a “placebo” or “low-dose” computer program, which was similar to the treatment program except its difficulty level was not interactively adjusted and daily training amounted to less than     10 minutes per day.

Training program

All training programs were written in the C programming language.

Visuospatial working memory task: The task involved the immediate serial recall of visuospatial information. Children were presented with six matrixes at 5 cm × 5 cm, with 3–5 colored squares in various positions (two matrixes for each of the three, four, or five square conditions). After the matrix had been removed, the child was asked to remember the positions of the colored squares and to point them out on an identical blank matrix^{[21, 28]}.

Visual verbal working memory tasks: For the training task, we used a similar paradigm to the one described by Miller et al ^[29]. The tasks in this paradigm are designed to reveal the nature of the working memory codes individuals rely on when asked to temporarily retain written words. Characters are selected from textbooks used in grades one to five. The average frequency of the characters was 17.64 per million, and the average number of strokes was 8.21. The participants were shown sequences of unrelated single target words, one after another on a computer screen. Immediately thereafter, they were asked to memorize a sequence of the first three target characters. Five Chinese characters were presented sequentially and displayed in a set order followed by a blank interstimuli presentation interval. The probe was three characters in the middle of the computer display. Only when both the orthography and order matched the three target characters was the subject supposed to press their index finger to indicate “yes” (A key of computer keyboard), otherwise, they were supposed to press their middle finger to indicate “no” (L key of computer keyboard). The tasks fell under a phonological condition designed to track reliance on a phonological memory strategy (Figure 1A), a visual condition designed to track reliance on a visual- perception-based memory strategy (Figure 1B), and a control condition (Figure 1C). In the phonological condition, the fourth characters resembled the target words phonologically, and were visually similar to those in the visual condition. The fifth characters were the distracter characters, and had no shared semantic, categorical, or linguistic features with the target words in any condition. Each condition was based upon 50 trails.

Central executive tasks: An inhibiting task is an often used version of the task used in this study^[30]. Participants are required to give a fast left- or right-hand response to a central target arrow during presentation of congruent flanker (i.e., target arrow and flankers associated with the same response) or incongruent flanker (i.e., target arrow and flankers associated with different responses) arrows. No responses were required for non-target, octagon figures presented instead of the target. The flanker arrows were presented before the target arrow. The participants received 150 trials consisted of 50 congruent flankers, 50 incongruent flankers, and 50 octagon figures.

Tests for the evaluation of the training

The study was a double-blind study where children, parents, and the psychologist administrating the baseline  and post-training tests were blinded to the version of the computer program the children had practiced, and to the expected effects of the two versions. All training was completed in a quiet room in the school, in small groups of five children supervised by a training aide who was a paid research associate. Evaluation included nontrained working memory measures and reading achievement.

Working memory measures:

(1) Verbal working memory:

(a) Digit span task

The digit span task is one of the tasks most often used to measure verbal working memory. It is part of the Wechsler Intelligence Scale for children, including the digit span forward task and the digit span backward task. In the first part, the digits are repeated in the same order as presented. In the second part, the child is asked to repeat the digits in the reverse order. The score corresponds to the maximum length of the item set recalled in the correct order of presentation.

(b) Word span task

For the purpose of measuring children’s verbal working memory for words instead of numbers, a word span test was used^[31-32]. It consisted of a series of frequently occurring Chinese words. Administration of the task and the scoring method were similar to those used for the Digit Span Subtest from the Wechsler Intelligence Scale for children.

(2) Visuospatial working memory:

Corsi span task

This is a well-known task, very frequently used to measure short-term memory for spatial sequential information^{[11, 13, 33]}. In addition, the task is considered to involve the encoding of visual stimuli, the retention of information over time, and response selection, prior to overt response execution^[34]. From two up to nine lamps were presented sequentially in a 3 × 3 grid. These lamps were illuminated successively, and each child was asked to recall the correct order by clicking the appropriate location with the computer mouse. The number of Lamps in the sequence was successively increased until the subject missed two trials in a row. The score was the maximum number of lamps remembered.

(3) Central executive function:

Stroop task

The Stroop task was used as a test of response central executive. Words describing colors were printed with ink in a color that was incongruent with the word. For example, the word “green” printed in yellow ink. The subjects were asked to name the ink color for each word. The time and accuracy for reading all 60 items was noted^[35].

(4) Reading achievement:

(a) Phonological task

Phonological awareness was measured by the children’s accuracy and mean reaction time on correct responses on the visual rhyming task. The visual rhyming task we used was similar to the paradigm described by Grossi  et al ^[36]. It contained 35 pairs of rhyming words and 35 pairs of nonrhyming words. Subjects needed to decide whether two sequentially presented written words rhymed or not. Each pair matching the average frequency of the characters and the average number of strokes selected from the textbooks used in grades one to five. The maximum score was 70.

(b) One-minute tests of reading words

This task were similar to Li and colleague’s reading ability task^[37]. 100 Chinese characters in the test were selected from textbooks that were used in primary schools for first to third graders, divided into 10 rows and 10 columns. Children were asked to read the characters aloud as quickly and accurately as possible within 1 min. Accuracy and reading fluency were scored.

Statistical analysis

Performance on non-trained working memory tasks and the two literacy measures is provided as mean ± SD. Paired-samples t-tests were conducted to evaluate group differences. Effect sizes were calculated using Cohen’s effect size formula^[38] (d), where an effect size of 0.20 is considered small, an effect of 0.50 medium, and an effect of 0.80 large. Furthermore, we conducted correlation analyses and regression analyses to determine the training effects. SPSS version 13.0 for windows software (SPSS, Chicago, IL, USA) was used for statistical analysis.  

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1  中文摘要

人们普遍认为，发展性阅读障碍的核心缺陷是语音意识障碍。但是一些研究发现，语音缺陷并非核心缺陷，而只是发展性阅读障碍的外显表现，反应的是更深一层的认知缺陷——工作记忆的缺陷。虽然工作记忆容量传统上被认为恒定不可改变的，但是近年来的研究证实，通过适合的、密集的训练，工作记忆能力可以得到提高。实验采用双盲法设计阅读障碍安慰组15人，阅读障碍干预组15人，采用一套自行设计适合中国儿童的计算机训练程序对其进行为期5周的工作记忆干预训练。探讨工作记忆和汉语发展性阅读障碍儿童语言技能的关系；通过对干预组阅读障碍儿童一定强度和频率的工作记忆训练后，其未训练的工作记忆任务的迁移效果以及押韵任务、阅读流畅性任务是否得到改善。结果显示，干预组阅读障碍儿童在未训练的视空间工作记忆任务、言语工作记忆任务和中央执行功能任务上均得到明显提高，差异有统计学意义。更重要的是通过训练，干预组阅读障碍儿童的视觉押韵任务和阅读流畅性任务明显改善。并且，工作记忆任务的提高与语言技能的改善相关。实验结论，工作记忆是汉语发展性阅读障碍儿童的阅读关键因素之一，通过改善工作记忆能力可以一定程度上使阅读障碍儿童的语言技能得到提高。

2  实验设计

目前国内外工作记忆对儿童的干预训练研究主要集中在对发展性阅读障碍儿童、学习困难儿童和正常儿童。文章根据汉语阅读障碍儿童的特点，针对汉语象形字的特点，增加了汉字材料的视觉言语工作记忆训练材料，自主设计了一套工作记忆训练程序。采用双盲法设计：干预组15人，每周5d，每天40min左右，持续5周的训练时间。针对儿童训练情况，通过改变各训练任务反应时间调节训练难度，同时给予正强化鼓励巩固训练效果；安慰组15人，每周5d，每天10min，持续5周的训练时间，不做训练难度调整和正强化。结果证实，阅读障碍干预组儿童的工作记忆可以提高，明显的训干预迁移效果在视觉押韵任务和阅读流畅性任务也得到反应。并且，越低水平的任务，改善越明显。

3  与国内外研究比较

目前国内外研究尚无针对阅读障碍的儿童的工作记忆干预实证性研究，同时尚缺乏一套不同于拼音文字的，适合汉语特点的阅读障碍工作记忆训练程序，实验增加了汉字材料的视觉言语工作记忆训练材料，自主设计了一套工作记忆训练程序。对于汉语阅读障碍儿童工作记忆的干预研究，既能很好的证明阅读障碍与工作记忆之间的因果关系，又是一个很有应用价值的研究方向。因此，如何对儿童的工作记忆进行干预将是该领域研究的重要趋势。