How Fast is Fear?

The minimum latency of potentiated startle after delay and trace fear conditioning was investigated. Delay conditioning is hypothesized to be mediated by automatic processes, whereas trace conditioning is hypothesized to involve controlled cognitive processes. In a group receiving delay conditioning, a tone conditioned stimulus (CS) signaled an electric shock unconditioned stimulus (US) presented 1,000 ms after CS onset. In a group receiving trace conditioning, a 200 ms tone CS was followed by an 800 ms gap prior to US presentation. Two control groups received unpaired CS/US presentations. It was hypothesized that fear-potentiated startle should be observed at shorter time intervals after CS onset in the group receiving delay conditioning compared to the group receiving trace conditioning. The results showed increased startle at 100 and 150 ms after CS onset in the group receiving delay conditioning compared to the unpaired group. In the group receiving trace conditioning, increased startle was observed at 1,500 ms after CS onset compared to the unpaired group. This supports the idea that conditioned fear after delay conditioning may be due to automatic processes, whereas trace conditioning is dependent on controlled processes.