Background stimuli and the inter-stimulus interval during pavlovian conditioning

An experiment was carried out to investigate the part played by background stimuli during Pavlovian conditioning. Groups of rats were presented with tone CSs and unavoidable footshock USs. Two components of the inter-stimulus interval, namely CS duration and the duration of a trace interval, were manipulated across groups. Subsequently subjects were tested for their reactions to background stimuli by being re-exposed to the training environment in the absence of both the CS and US. The degree to which rats failed to avoid this environment was found to relate to CS duration by an inverted U curve. The manipulation of the trace interval however did not significantly affect avoidance.