Study On The Causes And Subtypes Of Developmental Dyscalculia

Since the concept of developmental dyscalculia(DD)has been put forward,this field has attracted more and more researchers’ attention.The rate of developmental dyscalculia children is about 6% in china.As so far,the definition of DD is not clear,most researchers believe that DD refers to those students whose intelligence is normal and in a normal teaching environment,with a low level of Mathematical achievement in the same group and failing to meet the requirements of the state’s math syllabus.Meanwhile,the low achievement is not lead by family society,growth and development and other reasons.The purpose of the present study was to explore the causes of DD and distinguish subtypes of DD based on differences in general and number-specific cognitive processing deficits observed in a DD sample at the same time.At present,there are two kinds hypothesis about the reasons of DD: The hypothesis of a domain general cognitive deficit and Hypothesis of domain specific deficits in number processing.The former suggests that the general cognitive abilities of DD(eg,working memory、executive function)is impaired;the latter suggests that DD is mainly poorer than the normal children at the basic number of processing.There are four main types of representative deficits in the field: object tracking system(OTS)deficit hypothesis,the approximate number system(ANS)deficit hypothesis,numerosity coding theory and the access deficit hypothesis.168 school children attending 8 schools participated in the study through two-step screening test.The study chose the sample from about 1600 pupils at Grade two and three of elementary in Chongqing.There are 80 girls and the sample was divided into two groups(the developmental dyscalculia group and the normal development group).And DD was about 80 pupils.All children were required to do the Raven Test and Block Design and Vocabulary of the Wechsler Intelligence Scale for Children-Fourth Edition(WISC-Ⅳ).They were administered to obtain measures of nonverbal and verbal IQ.The screening test also measure their reading and math achievement by standard achievement test.The test groups were sampled through screening tests firstly,then the study decided the finally school children combing teacher’s recommendation.The purpose of the first study was to explore the causes of developmental dyscalculia.Both of the two groups accepted 19 tasks and they reflect general and number-specific cognitive functions.There are 13 cognitive tasks and 6 basic number processing tasks.19 measures include: rapid naming,attention task,graphics construction,psychological rotation,working memory,execute function,reasoning task,number line,dot magnitude discrimination,finger perception task,subitizing and number(digits)magnitude comparison.These tasks involve two forms: pencil-and-paper test and computer measuring.The results are recorded by the objects’ response in both reaction time and accuracy.The results show that the performance of DD children was worse than normal children in the following tasks: Stroke、Graphics Sequence Task、Transitive Inference Task、Digit Span、Non-symbolic Comparison Task、Number Line and More-odd Shifting Task.The purpose of the second study was to distinguish subtypes of DD.According to first study,the performance of DD children was worse than normal children in seven tasks.But the study found something wrong about More-odd Shifting Task.Although the DD children’s response in accuracy was worse than normal children,the DD children’s response in reaction time was better than normal children.The normal children spent much time to improve the accuracy.The results of this task didn’t enter the study next.So DD children’s scores on the six individual cognitive or number-specific processing tasks were entered as variables in the cluster analysis.And there are 62 DD children’s scores entered the cluster analysis.There are three different clustering approaches including average linkage、ward’s method and complete linkage.All the latent variable scores were transformed into standardized z-scores to ensure that differences in measurement scale did not influence the results.Finally the results revealed four distinguishable clusters of DD children.Cluster one is good at all the measures;cluster two is only impaired at transitive inference;cluster three is impaired at ANS,working memory,transitive inference and attention;and cluster four is impaired at almost of the measures.The study found the following two main conclusions:(1)DD might be caused by multiple deficits and not only a single core deficit.The DD group displayed weakness with most cognitive functions(e.g.,attention,working memory)and two aspects of number processing(e.g.,number-line estimation,non-symbolic magnitude comparison).These findings favor the defective approximate number system(ANS)and the domain general cognitive deficit hypothesis.(2)DD is a heterogeneous disorder,and there are different subtypes.Different subtypes of DD children show different defects and most DD children have more than one defect.