An Event-related Potentials Study Of Representation And Processing Of Categorization

Categorization is a basic cognitive ability which is to classify objects intodifferent categories by different standards. Categorization is a complex procedure. Itcontains the procedure of selective attention and processing, forming and applyingsome standards and classify objects. In the studies of classification, there are twomain points arguing about the representation of objects in categorization. That aredomain-specific theory and modality-specific theory. And whether the category effectis effected by different tasks is another point being focused on in this field. In ourstudy one we focused on the above two aspects. Pictures of birds, chairs andgeometric figures were used as stimuli. The participants were asked to respond tothese three different targets in three tasks.So we could compare birds and chairsstimulus as targets and non-targets(which were in the task of responding to thegeometric figures) under different conditions. We studied four ERP components,including N1, P1, N2, P2. Results are as follows. (1)Differences of P1, N1 and P2were found of the same category stimulus under target and non-target conditions.(2)Category difference of N2 and P2 were found of different stimulus. (3)Sourceanalysis showed brain area difference which supported domain-specific theory.Up till now, the studied about categorization has maily concerned the procedureof classifying objects, which make the forming mechanisms of categorization seemsunimportant. However, it is not. The forming of categorization is to form thestandards of classifying through some strategies by learning and concluding thefeatures of stimulus. Furthermore, in this field, the features of stimulus is important,for example, the common stimulus we used like artificial objects and natural objectscontains not only perceptual features(e.g.shape) but also semanticfeatures(e.g.function). Our study two concerned the perceptual features during theinduction and forming of the categorization by using geometric figures as stimulus(which could preclude the semantic components of the stimulus and made thestudy purer).The basic task is letting the participants decide whether the third stimuliis identical with the first two presenting in a series which share some same features.This consideration was for studying the stimulus processing during the forming ofcategorization. Also there were two tasks with different number of the categorystandards which was for the study of the number effect and the categorizationspeciality of the adults. Components of N120, frontal selective positivity, parietalselective negativity, N300 and P450 were analysed. Resuls were as follows. (1)Thestimulus' feature were kind of selectively processed during the forming procedure ofcategorization. (2)Adults preferred to froming and using rules as standards duringcategorization which was different with the adolescence who preferred to usingsimilarities. (3)P450 was under task effect.This study thoroughly discussed the representation and processing of thecategorization.