Effects of inter-trial interval on sign-tracking and conditioned reinforcer efficacy in female rats

Previous nonhuman studies have reported that sign-tracking to a conditioned stimulus (CS) is increased when the intertrial interval (ITI) duration is increased. Separate studies indicate that individual differences in sign-tracking (vs. goal-tracking) at a fixed ITI (and CS duration) is predictive of the conditioned reinforcer efficacy of the CS. The present study evaluates, for the first time, if increasing the ITI increases rats' sign-tracking and the conditioned reinforcing efficacy of the CS. Forty-five female rats were randomly assigned to one of three groups that completed appetitive Pavlovian training with ITIs of 14, 24, or 96 s. Subsequently, they completed tests of conditioned reinforcement. Replicating previous findings, longer ITIs increased sign-tracking to a lever-CS and, extending the literature, conditioned reinforcer efficacy of that CS was highest at the longest ITI used during Pavlovian training. Implications for behavioral interventions using conditioned reinforcement are discussed.