Witnessing a traumatic event can produce the same fear response as experiencing the event itself, according to a new study by researchers at New York University. The findings broaden our understanding of Pavlovian fear conditioning by revealing that it applies not only to directly experiencing an event, such as being bitten by a dog, but also to witnessing one. The findings appear in the December issue of Psychological Science, published by the American Psychological Society.

This study, by NYU graduate student Andreas Olsson and Psychology Professor Elizabeth Phelps, provides the first systematic comparison of fear learning through Pavlovian conditioning, social observation, and verbal instruction.

“Pavlovian fear conditioning shows that most species can learn to fear an object after it coincides with a naturally aversive event,” explained Phelps. “However, these results confirm that humans have indirect means to learn from others that are both faster and considerably less risky.”

“These findings are consistent with a recent line of studies reporting that observing somebody else in pain engages parts of the brain that are also involved in self-experienced pain,” added Olsson. “Our results extend this line of research to emotional learning and indicate that the fears acquired through social observation are similar to those acquired through direct aversive experience.”

In conducting the research, college students were placed into three groups. The first, the Pavlovian conditioning group, received a mild shock paired with a face. The second, the social observation group, learned through observing the emotional expression of another person receiving a mild shock paired with the face. The third, the instructed learning group, was told that the face predicted a mild shock. No shocks were given to participants in the observation and instructed learning groups.

All groups demonstrated a physiological arousal response, consistent with fear, when they saw the face that had been linked with a shock or a threat of a shock. Consistent with previous research, the Pavlovian conditioning group also displayed a fear response to the “threatening” face when the face was presented subliminally (i.e., so quickly participants were unaware of its presentation). However, the observation group also showed this effect, while the instructed group did not.

“Pavlovian and observational learning, which humans share with other primates, might be supported by an evolutionarily old system that predates the emergence of language,” Olsson and Phelps wrote in the paper. Learning through verbal instruction may depend on a mechanism in the brain that evolved after the old system, they added.

These findings shed light on how fears are socially communicated and have implications for understanding how cultural knowledge is acquired and may influence other behaviors, such as decision making, memory, and psychopathology.

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