An ERP Study Of Children With Mathematical Learning Disability In Simple Mental Calculation

Mental calculation is an arithmetic operation in the absence of other tools (such as pen and paper, calculators, etc.). The problems like 6+7 and 5×6 belong to the simple mental arithmetic. The results which are stored in long term memory as arithmetic facts can be directly retrieved. Numerical distance effect and numerical notation effect are the important phenomena in mental arithmetic processing. As the name implies, the distance between two numbers influences the comparison of the stimuli: the smaller the distance, the longer the reaction time. Generally, the performance of word number symbols in a variety of verbal format is worse than the performance of Arabic number symbols in visual format, this is the so-called numerical notation effect.Mathematical learning disability (MLD) is one type of learning disabilities. MLD children have normal intelligence, but the ability to learn about the mathematical skills significantly lag behind the normal children in the same age. Previous studies had found that these children had deficit in numerical distance effect and developed slowly in converting number notations, but the reasons were unclear. ERP technology can record the EEG during simple mental arithmetic: N270 is the electric signal of cerebral cortex for processing conflict information; P300 mainly reflects the overall recognition to the number significance of mental arithmetic. Numerical distance effect and numerical notation effect can be reflected in the changes of N270/ P300 latency and amplitude. It was hypothesized that MLD children had deficit in numerical distance effect and were abnormal in numerical notation effect. These were due to the insufficiently spatial representation of magnitude and encoding mechanism of verbal number. Two ERP experiments were designed to test MLD and normal children (control group) in grade 3 to verify these hypotheses.Experiment 1 employed the simple mental calculation task of Arabic number. Electrical Geodesics Incorporated system was used to record the response time, latency, et al. The statistics analysis showed: the speed of retrieve arithmetic facts in MLD children was slower than control group and the reasons were probably the deficit in the ability to inhibit irrelevant information from entering working memory and the difficulty to identify the overall number property; compared to control group, MLD group did not show numerical distance effect, which suggested that they had difficulties in spatially representing number magnitude; the topography result showed that MLD children had deficit in right hemisphere.The simple mental calculation task of Chinese number word was used in Experiment 2. The results indicated: the MLD children had difficult in the speed of retrieve arithmetic facts; the numerical distance effect disappeared in MLD group, which suggested that they had deficit in the mechanism of encoding verbal number; parietal lobe was the advantaged region to represent the magnitude of verbal number and MLD children had deficit or delayed development in the area.The comparison of two number notations suggested: the processing speed of Arabic number was faster than Chinese number word in the parietal region, which showed the significant numerical notation effect; there were differences between MLD group and control group in numerical notation effect, which suggested that MLD children had slower speed in processing verbal number and had deficit in translating ability of magnitude representation.Conclusively, the ERP research on simple mental calculation in MLD children and normal children confirmed all the hypotheses. In the simple mental calculation processing, MLD children had deficit in numerical distance effect and abnormality in numerical notation effect. This study enriched the understanding of simple mental arithmetic processing of MLD children in theory, and revealed the possible reasons for the deficits. These findings may benefit the education practitioners in that it may help teachers recognize and understand the mental calculation problem in MLD children and make appropriate and necessary intervention.