| As an important part of mathematical cognition, numerical estimation is a pervasive process in the daily life of both children and adults. It refers to a rough estimation when people have no enough time to count the quantities of objects, or counted quantities are excessive, or can't count the moving objects at all. Cognitive style refers to the individual differences brought out during the course of organizing and processing information, which is a psychology concept between intellectual power and personality. Estimation was paid more and more attention since 1980s. So did numerical estimation. But it is noticeable that, there is still no researcher to investigate the relationship between numerical estimation and cognitive style. And as the development of neural electrophysiology and computer technology, psychologists begin to study the neurophysiological mechanism of brain on estimation. Some new technologies, such as EEG, fMRI and ERP, are widely used as the objective and effective research means. Especially, the ERPs technology is a valuable means to research cognitive processes ( eg. perception, attention and memory) and cognitive functions. This research discusses the influence of various tasks presenting modes on undergraduates'numerical estimation with different cognitive styles on the basis of behavioral data, and also investigate their electroencephalographic activities in the numerical estimation task by ERPs technology.This research included three experiments. One of them is a preliminary experiment to investigate the stimuli-presenting time and insure subjects to make the reasonable estimation. And the others include numerical estimation experiment and ERP experiment, which respectively investigate the difference of three numerical estimation task on different cognitive styles undergraduates and electroencepha- lographic activities in numerical estimation tasks.The results showed that:(1) There were no significant differences in RTs among three conditions and large-small numbers of numerical estimation between the field-dependent individual and field-independent individual. But RTs of field-dependent individual were longer than that of field-independent individual,, and RTs of large-numbers were longer that of small-numbers.(2) The correct percents of field-independent individual were higher than that of the field-dependent individual. But on the whole, there was no significant differences of cognitive style between the condition of pure targets stimulus and distractor number the same as targets. But there was significant differences between them in the condition of distractor number twice as targets.(3) The result ofχ~2 test showed that there were no significant difference between the field-dependent individual and field-independent individual under three conditions (underestimation, overestimation, reasonable estimation). And neither did the estimation of large-small numbers.(4) In the condition of pure targets stimulus, the field-dependent individual was inclined to using logarithmic representations, but the field-independent individual was apt to use linear representations. But in the condition of distractor number the same as targets and in the condition of distractor number twice as targets, they are all inclined to use logarithmic representations, and the field-dependent individual showed more distinct in this tendency.(5) Different cognitive style individuals were inclined to using grouping strategy, fore-and-aft comparison strategy, global perception strategy and numerical preference strategy et al. But the field-dependent individual used more fore-and-aft comparison strategy than the field-independent individual, and the field-dependent individual used more global perception strategy.(6) The results of ERP data showed that: in the components of N1,LPC, the condition of stimulus had great main effect. The large-small factor had main effect in the component of N1, and there were main effects for the electrodes in the three components. In the three conditions, there was obviously negative electro-activity about 400ms-450ms in frontal lobe and central lobe for estimating the large-small factor. But there was obviously positive elecro-activity about 300ms-350ms in central lobe among three conditions. The N1,P1,LPC amplitudes were largest in the condition of targets stimulus. And the P1 amplitude was larger in small-number task than in large-number task.To sum up, the following conditions were drawn:(1) There were no statistically significant differences in RTs, correct percents, reasonability and representations of numerical estimation between different cognitive style undergraduates in the different stimulus conditions and large-small number factors. (2) There were obviously electroencephalographic activities in frontal lobe when individual estimated the numerical estimation tasks in different conditions. In three conditions, there was obviously negative electro-activity about 400ms-450ms in frontal lobe and central lobe for estimating the large-small factor. But there was also obviously positive elecro-activity about 300ms-350ms in central lobe among three conditions.
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