Abstract: This paper explores 6-year-old children’s category representation and learning strategies. Category learning is a fundamental ability through which human beings acquire and organize new knowledge about the world (Ashby, 2005), and is critical for normal cognitive development.
There are three major theories or models of how categories are represented: Rule-based, Prototype-based, and Exemplar-based models. Rule-based models assume that category learning is a process of discovering an explicit rule to maximize accuracy (Ashby, 2005; Seger, 2006). Prototype-based models assume that stimuli are categorized on the basis of their similarity to category prototypes stored in memory (Rosch & Mervis, 1975; Smith, Chapman, & Redford, 2010; Coutinho, Redford, & Smith, 2010). A category prototype is generally defined as the average, or most typical, member of a category. Exemplar-based models assume that the categorization of a new exemplar is based on the similarity of the new exemplar to the representations of all previously encountered exemplars stored in memory (Medin & Schaffer, 1978; Kruschke, 1992; Nosofsky, 1992).
Previous studies suggest that 6-year-old children have developed some ability to use category knowledge to solve problems (Wilburn & Feeney, 2008; Sloutsky & Lo, 1999; Sloutsky & Fisher, 2001). Furthermore, several critical aspects of category learning are acquired at this age. Fang, Fang, & Xi (1991) pointed out that 6-year-old is a critical period for children to learn to understand the relation between the whole and the part of a subject. Yin (1996) further suggested that 6 years is an important age to learn superordinate categories (for example, the category “furniture”).
Two category structures were used in this study. Experiment 1 used the “5/4 category structure” from Medin and Schaffer (1978) and experiment 2 used the “3/3 category structure” from Yamauchi, Love, & Markman (2002). The category structures were adapted in order to be able to identify which kinds of representation the children were forming: rule, exemplar or prototype. 62 6-year-old children took part in the experiments. During each trial, an individual exemplar was presented, the participant was asked to infer and indicate which category (A or B) the exemplar belonged to, and feedback as to whether the subject was right or wrong was provided. After a number of such trials of inference and feedback, participants reached the learning criterion and were considered to have formed new category knowledge. A mathematical technique of “Model Fitting” was introduced to analyze the data from two experiments. Different models were used to examine whether childrens’ responses were best fit by exemplar or prototype models, to identify which features the children paid attention to, and to identify which classification strategy children used.
Experiment 1 showed that 6-year-old children were able to learn the 5/4 categorization task and reach criterion. Model fitting analyses of category representation found that these children tended to form exemplar representations rather than prototype representations. On measures of distribution of attention, 6-year-old children could identify and pay more attention to the more typical dimensions. Finally, when learning strategy was examined, 6-year-old children used either a single-dimension or rule-plus-exception strategy to classify the items. Experiment 2 using the 3/3 task found similar results to experiment 1, but further found that 6-year-old children could not integrate their processing of the most important distinctive dimensions across the two categories. This result was consistent with the findings of Inhelder & Piaget (1958), and Anaki & Bentin (2009) that 6-year-old children could not process information across different categories.

Key words: category learning, children, prototype, exemplar, categorization strategy