The Changing Composition of Abstracted Categories Under Manipulations of Decisional Change, Choice Difficulty, and Category Size

The role of decisional factors in category abstraction was investigated. The major prediction was that a change in instructional set would primarily affect the more difficult choices of a category (boundary contraction hypothesis), with this outcome modulated by category size. Subjects classified patterns into three prototype categories until they reached an errorless criterion; then they immediately took a transfer test under a conservative or liberal set. Category size was varied independently of category frequency in Experiment 1; in Experiment 2, category size functioned as a between-subjects variable. The results showed that instructional set affected new, but not old, instances, with this effect additive across choice difficulty and category size. The boundary contraction hypothesis was rejected, and a two-stage model of classification was proposed to account for the results. A compositional analysis revealed that far greater levels of learning may be needed before selective decision making can occur.