The Cognitive And Developmental Mechanisms Of The Representation Of Similarity Between Objects

When interacting with the environment, human beings categorize them by simple and economic principles by. The categorization process can remarkably increase the efficiency of cognition as it lends itself to orderly and quickly encoding, storing and retrieving immense and complicated information. The similarity-based categorization is one of the most common ways to classify information and lays the basis for many other categorizations, such as concepts. Similarity refers to common features or structures between perceived objects and the representation of its prototype categorization, based on which humans can obtain the essential relationship of the world. Few studies so far have been done to explore the mechanism of the similarity-based representation, even though a couple of researches about categorization mentioned this issue. Also there exist several researches which specialize in the similarity-based representation, but the research objects are the brain mechanism on primates. The core and basic role of the similarity-based representation in induction and reasoning cognition motivate us to examine its mechanism deeply and systematically. On the basis of prior studies, six experiments have been done in the present research to explore the mechanism of the similarity representation of objects in human beings in a developmental perspective with using psychophysical, electrophysiological methods.In experiment 1,430 animal pictures were selected from the internet and were decolorized so that to make them look black and white.60 pairs of pictures met the requirement of candidate pictures by matching the similarity of their shapes and the position of the key features.40 college students were asked to evaluate the similarity of the candidate pictures according to the familiarity, similarity of the shapes, similarity of the profiles and the position of the key features.23 pairs of pictures met the final requirements and 10 pairs which ranked higher scores were chosen as the standard pictures for the following experimental materials.In experiment 2,8 symmetrical pictures were generated as stimulus pictures based on the different levels of similarity (90%,80%,70% and 60%) to the standard pictures for each of the 10 pairs using Morph technique.50 college students (25 males and 25 females) participated in the experiment and were asked in each trial to judge which of the two standard pictures was more similar to a stimulus picture as quickly and accurately as possible. Reaction time and responses were recorded.2 standard pictures and the corresponding 8 morphed pictures were contained in each of the whole 10 blocks. The results showed that the reaction time while decreased and the accuracy rate increased as the similarity between the stimulus pictures and the standard pictures increased. Curvilinear regression analyzing indicated that quadratic function can explain the relation between the perceptual similarity of objects and the physical similarity of objects.In experiment3, ERP techniques were employed to explore the time course and the electrophysiological mechanism of the similarity representation of objects in adults.2 standard pictures and 9 symmetrical pictures which were generated based on the 5 levels of similarity (90%,80%,70%,60% and 50%) to the standard pictures were contained in the experiment materials.17 college students (7 males and 10 females) participated in the experiment. The procedure and the task were same as those in experiment 2. Consistent behavioral results with those in experiment 2 were obtained: The reaction speed and accuracy increased as the level of the similarity increased. The ERP data showed that N2 and P300 were sensitive to the similarity information:the levels of 50%,60%,70% elicited larger amplitude of N2 than the levels of 80%,90%, 100%. Interestingly, the level of 60% elicited smaller amplitude of P300 not only than the level of 50%, but also compared to the levels of 70%,80%,90%,100%, which seemingly indicated that the similarity level of 60% might be a turning point in the perception of similarity for humans. The results of dipole source analysis indicated that the posterior cingutate and parahippocampal gyrus might involve in the processing of similarity representation.Based on experiment 3,6 levels of similarity which were all closed to the level of 60% and differed from each other in the amount of 2% were employed as 6 conditions in experiment 4. The experiment procedure and the task were as same as those in experiment 2 and 3. Behavioral data showed that reaction time decreased significantly as the similarity level increased. In terms of the accuracy rate, no difference were found among the levels of 55%,57%,59%, but they were all lower than the levels of 61%, 63%,65%; No difference was observed between the level of 61%and 63%,63% and 65%, but the only difference was found between 61% and 65%. More importantly, interesting ERP results were observed:for the N2 component, the condition of 55%, 57%,59% induced smaller amplitude than the condition of 61%, at the same time, no difference were observed between the conditions of 61% and 63% both of which induced larger amplitude than the condition of 65%. As for the P300 amplitude, the conditions of 55%,57%,59% elicited larger amplitude than the condition of 61% did, at the same time, the condition of 65% elicited larger p300 amplitude than the condition of 61%. No difference was observed between 61% and 63%. Both the behavioral and the ERP results suggested that similarity levels around 61%-63% were likely to be the transition bound in similarity perception. When the similarity level was lower than 61%, people hardly recognized the picture as the prototype picture for a lack of sufficient information. While those levels which were higher than 65% contained enough information for people to correctly represent and recognize the morphed pictures.In Experiment 5 and 6, we explored the cognitive and electrophysiological mechanism of similarity representation of objects for children aged around 4-5 years old. The materials, the procedure and the task in experiment 5 were same as those in experiment 3. Forty-two 4-5 years old children (22 males and 20 females) participated in the experiment. The results showed the same behavioral pattern as that in experiment 3:the reaction time decreased and the accuracy rate increased as the similarity between the stimulus pictures and the standard pictures increased. Also, curvilinear regression analysis indicated that the relation between the perceptual similarity of objects and the physical similarity of objects conformed to quadratic function. To further examine the patterns between the children and the adults, we compared the behavioral results of adults in experiment 3 and those of children in the experiment 5. As a result, it was found that children responded slower than adults did, which might be due to the fact that it took longer time for them to press the keys. More importantly, the accuracy rate for the children was higher than that for the adults only when the similarity level was 60%, which suggested that neither children nor adults could discriminate objects in the perceptual level when the similarity level were around 50%; It seems children could perceive more similarity information than adults when the level was 60%. However, the advantage disappeared when the level was higher than 70% as both of the groups could easily obtain enough information for the similarity perception. The results suggested that children were better than adults to perceive similarity information especially when limited information was available. The reason might be that the two groups adopted different strategies:children were more likely to categorize objects based on perceptual similarity while adults were more likely to categorize objects based on abstract concepts.In experiment 6, we further explored the cognitive mechanism of the similarity representation of objects for children by applying the same experiment materials, procedure and task. In addition, forty-two 4 or 5-year-old children participated in the experiment (16 males and 26 females). The results showed that the reaction time decreased as the similarity level increased. The maximal and minimal decrease amounts were found respectively between the level of 59% and 61%. Meanwhile, the difference of the accuracy rate were observed among all the levels except between the level of 63% and 65%, among them, the increase amount reached highest between the levels of 55% and 57%. No difference was found for the increase amount between any other following two consecutive levels. Finally, we statistically compared the behavioral data in experiment 6 and the one in experiment 4. The results agreed with the comparison results betweent the experiment 3 and 5:children reacted faster than adults in all levels of similarity. As for the accuracy rate, no difference was observed when the rate was 55%. And children perceived more accurately than adults when the level of similarity was 57%. A marginally significant difference was found between the two groups when the level was 61%,63% and 65%. The pattern further confirmed the results obtained in experiment 5:When the level of similarity was lower than 55%, hardly could any people recognize the objects and when the level was around 57%-61%, children demonstrated better capability to perceive similarity than adults; And when the level reached 61%-65%, the difference between the two groups disappeared. It is possible that the similarity level should at least reach 65% for people to stably perceive the target-object as some prototype object when representing the similarity of objects.To sum up, in the present research, we find that the relation between the perceptual similarity of objects and the physical similarity of objects conform to quadratic function; 4-5-year old children are better to perceive the similarity of objects than adults do, especially when the similarity is 57%-59%. When the level of similarity is lower than 55%, hardly can any people recognize the objects and when the level is higher than 65%, both children and adults are equally able to perceive objects correctly; The ERP component N2 and P300 are sensitive to the similarity representation. Furthermore, a hypothesis needs to be inspected in the future research in which the posterior cingutate and parahippocampal gyrus might be involved in the processing of similarity perception.