Stimulus typicality determines how broadly fear is generalized.

The ability to represent knowledge at the category level promotes the transfer of learning. How this ability integrates with basic forms of conditioned learning is unknown but could explain why conditioned fear is overgeneralized after aversive experiences. We examined the impact of stimulus typicality--an important determinant of category-based induction--on fear learning and generalization. Typicality is known to affect the strength of categorical arguments; a premise involving typical exemplars (e.g., sparrow) is believed to apply to other members, whereas a premise about atypical exemplars (e.g., penguin) generalizes more narrowly to similar items. We adopted this framework to human fear conditioning and found that fear conditioned to typical exemplars generalized more readily to atypical members than vice versa, despite equal feature overlap across conditions. These findings have implications for understanding why some fearful events lead to broad overgeneralization of fear whereas others are regarded as isolated episodes.