Stimulus diversity increases category-based fear generalization and the effect of intolerance of uncertainty.

Fear generalization refers to conditioned fear responses extending to related stimuli and fear overgeneralization is a key feature of pathological anxiety. Along with perception similarity, conceptual relations affect fear generalization. We investigated whether stimulus diversity-an important principle of category-based induction-influences fear generalization. Induction studies have shown that generalization from a premise involving diverse instances is stronger than that from non-diverse instances. We adopted this framework for fear learning and established two groups. The diverse group developed fear in response to diverse instances from one category, while the non-diverse group acquired fear of non-diverse instances from the same category. An effect of stimulus diversity was observed in shock-expectancy ratings, with the diverse group displaying higher fear generalization than the non-diverse group. We also tested whether intolerance of uncertainty (IU) might affect the difference in fear generalization between the two conditions. Individuals with higher IU showed reduced difference in fear generalization between two conditions, mainly driven by heightened fear generalization to novel stimulus with ambiguous threat levels in the non-diverse condition. This study helps illustrate the mechanisms behind differential category-based fear generalization and provides a potential explanation for why higher IU individuals may develop anxiety disorders following trauma.