The effect of partial and continuous reinforcement on the generalization of conditioned fear in humans

The popular paradigm of Pavlovian conditioned fear has been used to study learning and memory processes that mediate anxiety disorder. Fear extinction studies have often paired the conditioned stimulus (CS) and the unconditioned stimulus (US) on a subset of acquisition trials (partial reinforcement) to prolong extinction. However, there have been few studies on the effect of partial reinforcement and continuous reinforcement on fear generalization. To better understand the influence of the CS–US pairing rate on fear generalization, the experimenters used CSs paired with US at 50% (CS50), 75% (CS75), and 100% (CS100) during fear conditioning. A total of 66 participants, who were assigned at random to the different reinforcement rates, underwent fear acquisition and generalization tests on expectancy ratings and skin conductance responses. The continuous reinforcement group (CS100) showed a flatter generalization gradient, while the partial reinforcement groups (CS50, CS75) showed increased generalization magnitudes. These results suggest that the partial reinforcement extinction effect is related to threat intensity, whereas continuous reinforcement produces threat-sensitivity fear generalization, which has been used to explain the overgeneralization of fear. ● There are no significant differences among 50%, 75%, and 100% reinforcement in fear acquisition. ● Partial reinforcement led to stronger fear generalization. ● Continuous reinforcement led to a flatter generalization gradient. ● The intensity and uncertainty of threat affect fear generalization.