Learning to avoid threats often occurs by observing others. Most previous research on observational fear learning (OFL) in humans has used pre-recorded standardized video of an actor and thus lacked ecological validity. Here, we aimed to enhance ecological validity of the OFL by engaging participants in a real-time observational procedure (35 pairs of healthy male friends, age 18–27). One of the participants watched the other undergo a differential fear conditioning task, in which a conditioned stimulus (CS+) was paired with an aversive electric shock and another stimulus (CS−) was always safe. Subsequently, the CS+ and CS− were presented to the observer to test the OFL. While the friend’s reactions to the shock elicited strong skin conductance responses (SCR) in all observers, subsequent differential SCRs (CS+ > CS−) were found only when declarative knowledge of the CS+/US contingency (rated by the participants) was acquired. Contingency-aware observers also showed elevated fear potentiated startle responses during both CS+ and CS− compared to baseline. We conclude that our real-time procedure can be effectively used to study OFL. The procedure allowed for dissecting two components of the OFL: an automatic emotional reaction to the response of the demonstrator and learning about stimulus contingency.

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Learning to avoid threats often occurs through indirect experiences, for example, by observing the behavior of others. Most previous research on observational learning has used pre-recorded stimuli to induce learning. Here, we aimed to enhance the ecological validity of the learning situation by inviting two friends to serve as the 'observer' and 'demonstrator', respectively. The observer watched their friend performing a differential fear-conditioning task in real time. During the task, one conditioned stimulus (CS+) was associated with an electric shock (unconditioned stimulus, US) to the forearm of the demonstrator. Another stimulus (CS-) was always safe. Following the learning phase, the observer was presented with the CS+ and CS-, but without receiving any shocks. As an index of learning, we measured their skin conductance and fear-potentiated startle responses. While the US applied to the demonstrator robustly elicited strong skin conductance responses in the observers during the learning phase, subsequent differential skin conductance responses of the observers (to CSs presented directly) were dependent on declarative knowledge of the CS+/US contingency. Contingency-aware observers also showed elevated fear-potentiated startle responses during both CS+ and CScompared to intertrial intervals. Learning efficiency was lower than in previous studies. We conclude that observational fear learning involves two separable components: an automatic, non-specific emotional reaction to the response of the demonstrator (serving as a social US) and learning to predict stimulus contingency (CS+/US pairing). Ecological modifications proposed in the article mirror analogous rodent studies on vicarious fear conditioning.