The indirect modification of categorical knowledge.

The present study investigated whether the later learning of a category could affect the representation of other categories learned previously. Participants initially learned two or three categories, where each stimulus was composed of features that were distinctive to a category, shared with one or both of the other categories, or were idiosyncratic. When two categories were initially learned, a subsequent learning phase involved the learning of a third category that either shared distinctive features with categories learned previously, thereby discounting those features as diagnostic or was composed of features unrelated to the original categories. A common transfer test contained old, new, and prototype stimuli for classification, as well as critical items that revealed whether discounting of previously diagnostic features had occurred. The results revealed that stimuli assigned to a particular category in the two-category condition were assigned to the third category learned subsequently when the later learning discounted previously diagnostic features. These results suggest that later learning of a category can indirectly modify the representation of categories learned previously.