A visual generalization gradient of conceptual stimuli based on fear acquisition in visual and auditory modalities

This study investigates crossmodal fear generalization, testing whether conditioned fear spreads between different sensory modalities. Participants in the unimodal group were presented with visual stimuli-images of a sparrow (CS+) and a laptop (CS-)-while the crossmodal group received auditory stimuli-sparrow calls (CS+) and keyboard typing sounds (CS-). During the generalization phase, both groups were presented with conceptually similar visual stimuli (GSs) with varying similarity to the CS+ (e.g. high: Pigeon, moderate: Duck, low: Goat). Measures included US expectancy ratings, skin conductance responses (SCR), and functional near-infrared spectroscopy (fNIRS). Results showed successful fear acquisition in both groups, with significantly higher US expectancy ratings, SCR, and mPFC HbO activity for CS+ compared to CS-. Both groups exhibited a gradient effect during the generalization phase, with GSs that were more perceptually similar to the CS+ eliciting higher US expectancy ratings. These findings support crossmodal fear generalization and offer new insights into the overgeneralization of fear in anxiety disorders.