Reexamination of contextual conditioning with massed versus distributed unconditioned stimuli

Sprague-Dawley rats were placed in the black compartment of a 2 compartment choice apparatus and received a series of unsignaled footshocks at fixed intertrial intervals (ITIs), with ITI duration varied across groups. Contextual conditioning was assessed using place preference and freezing tests. In Experiments 1 and 3, time spent in the unshocked, white compartment in a preference test decreased monotonically with increasing ITI. In Experiment 2, less freezing occurred in the 3-s than in the 60-s groups. An inverted U-shaped relationship between ITI and freezing emerged when a full range of ITIs was used in Experiment 3. The results have implications for the learning-performance distinction and suggest that short ITIs may promote contextual conditioning.