Feature selection and classification: A developmental study

Two hundred and thirteen children between the ages of 4 and 16 sorted 30 complex objects freely into groups. These were either schematic faces, schematic imaginary animals, or histoform patterns and were constructed from 9 independently and continuously varying features, each with 10 levels. The three sets were equivalent in terms of underlying numerical structure. A new method of analysis of the groups formed yielded the following direct measures of subjective organization in the sorting of each child: the number of features used in sorting, the accuracy of sorting, and the number of independent dimensions of classification. Both the material and the analysis of sorting were devised on the assumption that only some of the component features of complex objects are used for classification, while others are ignored. Sorting performance differed markedly both with age and with different types of material. The improvement in sorting ability with age, except for the youngest children, could be attributed to an increase in the number of features used rather than an improvement in the accuracy of use. In contrast, the poor sorting of histoform patterns as opposed to faces and animals was due to a low level of sorting accuracy. The basic results on the development of classification confirmed previous studies, and hence suggest that it is valid to consider feature selection as a basic component of classification.