Learning includes the ability to generalize to new situations and respond to similar, yet not identical stimuli. We use stimulus generalization in humans to show that tones that were negatively reinforced induce wider generalization curves than tones that were positively reinforced, and these in turn induce wider curves than neutral memory. Importantly, these wider generalization curves persist even if outcomes for all tones are made identical, indicating that the learning induced a perceptual change, and not merely a decision bias. Moreover, it persists after taking into account loss-aversion, suggesting it is a result of valence per se, and not intensity that reflects overweighting of the aversive stimuli. This effect of emotional valence on learning suggests different locations of plasticity and network mechanisms in the brain. Particularly, it suggests that brain areas that mediate reinforcement and emotions are involved during the learning process to induce a neural representation that can support this broader behavioral generalization. In addition, these findings highlight a model for anxiety and trauma disorders in which aversive experiences affect more than they should, sometimes even in seemingly irrational situations.