The effect of feedback stimuli on contextual fear depends upon the length of the minimum intertrial interval

The present experiments investigated the effects of manipulation of the minimum intertrial interval (ITI) on the ability of a feedback stimulus to reduce the amount of fear conditioned to the shock context. In Experiment 1, we found that animals exposed to yoked shock with a feedback stimulus were equivalent to animals which received escapable shock, and both these groups showed less fear of the shock context than did yoked animals not given feedback, when a minimum ITI of 60 s was used. This replicated the effect of feedback on contextual fear conditioning. However, animals exposed to yoked shock with a feedback stimulus but for whom the minimum ITI was 5 s showed as much fear of the context as yoked animals not given feedback. Experiment 2 assessed whether this difference was solely due to the lower minimum ITI resulting in more fear than the 60-s minimum ITI, or whether the lower minimum ITI precluded the effect of feedback. The former possibility was discounted. Thus, these studies demonstrate that a relatively long minimum ITI is essential for the observance of a feedback effect on fear of the shock context.