Induction from a single instance: formation of a novel category.

This study examines whether preschoolers can use information from a known category to induce a characteristic attribute of a novel, contrasting category based on a single instance. We showed 32 four-year-olds three instances of a Given Category and one instance of a Target Category. These objects could vary along two attribute dimensions, such as color and shape. All instances of the Given Category shared identical values of one attribute (e.g., all were blue), but could have different values of the other attribute (e.g., a circle, a square, and a triangle). The single instance of the Target Category was different from the Given on both attribute dimensions (e.g., a red diamond). Children gave yes/no judgements as to whether additional objects were instances of the Target Category. There were two possible sources of information about the relevance of an attribute to classification: explicit (labeling) and implicit (variation in the Given Category). There were four conditions such that each source of information was either available or not. Both types of information were effective in eliciting inductions of the relevant kind of attribute and the characteristic value of this attribute in the novel category (explicit: p = .0004; implicit: p = .031). This suggests that children use an inductive bias that the instances of two related but distinct categories tend to be alike in the same way.

Countable entities: developmental changes.

The canonical countable entity for 3- and 4-year-old children is a discrete physical object. When children were asked to count labeled entities such as "forks", they counted each detached part of a fork as a separate entity. When asked to count kinds ("How many kinds of animals?") or properties ("How many colors?"), where each kind or property was exemplified by several separate objects, they included each discrete object in their count. Their counts of classes were more accurate in the absence of objects, or in the presence of a single member of each class, than in the presence of several members of each class. Young children are evidently predisposed to process discrete physical objects. Evidence is presented that, developmentally, this bias precedes learning to count. It is proposed that this discrete physical object bias facilitates mastery of counting.

The class-inclusion task: question form and distributive comparisons.

The class-inclusion task is regarded by Piaget as a measure of the child's mastery of the structure of hierarchical classification. Class-inclusion was improved by changing the wording of the question to conform to standard English usage. A theoretical argument is offered that the child's difficulties with this task derive from confusion of collective comparisons, in which properties of classes are compared, and distributive comparisons, in which properties of elements are compared. A grammatical constraint on expression of distributive comparisons--an element of a class cannot be compared to an element of an included subclass--is hypothesized to be overgeneralized to expressions referring to collective comparisons such as the class-inclusion task. This hypothesis accounts for the improvement in class-inclusion performance with changes in wording of the question and for the finding that young children's response to class-inclusion questions and to ungrammatical requests for comparison of an element of a class and an element of an included subclass are similar: the children respond readily but understand wrongly that the comparison involves coordinate classes.