Timing of interfering events in one-trial serial overshadowing of a taste aversion.

This set of experiments examined the question of when a stimulus would be most effective in overshadowing the acquisition of long-delay taste aversion learning. In Experiment 1 rats drank sucrose, the target solution, followed by a hydrochloric acid (HCl) solution before lithium injection some time later; HCl was presented either early or late in the interval. The late condition produced greater overshadowing than the early condition. The importance of the HCl-injection interval was confirmed by Experiment 2, in which the sucrose-injection interval was varied. Experiment 3 found that even placement in a different context - an event that normally produces little overshadowing of a CTA - produced one-trial overshadowing of a sucrose aversion as long as the context was novel and exposure to it occurred immediately before lithium injection. No current theoretical account of one-trial overshadowing predicts that a late event produces more overshadowing than an early event. This result can, however, be accommodated within a modified version of the Rescorla-Wagner model.