Rats acquired aversions to food pellets when a previously trained signal for that food was paired with a toxin, but only after minimal signal-food training. After extensive signal-food training, signal-toxin pairings had no effect on food consumption even after manipulations that enhanced the associability of the signal. By contrast, conditioned responding to the signal retained its sensitivity to devaluation of the food reinforcer by food-toxin pairings after extensive training. These results suggest that the nature of associatively activated event representations changes over the course of training.