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The generalization of conditioned fear responses has been shown to decrease as a function of perceptual similarity. However, generalization may also extend beyond the perceptual discrimination threshold, ostensibly due to contributions from processes other than perception. Currently the neural mechanisms that mediate perceptual and non-perceptual aspects of fear generalization are unclear.

To investigate this question, we conducted a Pavlovian fear conditioning and generalization experiment, collecting functional magnetic resonance imaging (fMRI), skin conductance and explicit shock likelihood ratings, in 37 healthy subjects. Face stimuli were initially paired (CS+) or not paired (CSsingle bond) with an electrical shock. During the generalization phase, responses were measured to the CS+, CSsingle bond and a range of CS + -tosingle bondCSsingle bond morphs (generalization stimuli), selected for each …