Variable shock-free times with informative and uniformative stimuli.

Three rats were trained on a fixed-ratio escape procedure in which responding produced one of two equiprobable outcomes-a 10-second or 60-second shock-free period. Before the fixed-ratio requirement was satisfied, brief shocks were presented at irregular intervals averaging either 15 or 30 seconds. Two conditions, differing in the relationship between exteroceptive stimuli and the outcomes, were studied. In the uninformative (uncorrelated) condition, the same stimulus was presented during both outcomes. In the informative (correlated) condition, one stimulus was present during the 10-second outcome only; another stimulus was present during the 60-second outcome only. Subjects pressed faster in the uninformative condition than they did in the informative condition. The inadequacy of the information hypothesis in accounting for the findings is discussed, and an alternative hypothesis is offered.