How transitions from nonrewarded to rewarded trials regulate responding in Pavlovian and instrumental learning following extensive acquisition training

In both discrimination learning and partial reinforcement, transitions may occur from nonrewarded to rewarded trials (NR transition). In discrimination learning, NR transitions may occur in two different stimulus alternatives (NR different transitions). In partial reward, NR transitions may occur in a single stimulus alternative (NR same transitions). Available instrumental learning data indicate that resistance to extinction is increased by both types of NR transitions following limited acquisition training. Following more extensive acquisition training, resistance to extinction appears to be increased by NR same transitions but not by NR different transitions. In Experiment 1, it was shown for the first time that following extensive acquisition training the effects of the two types of transitions are the same in the Pavlovian situation as in the instrumental situation. This finding indicates that on the current trial the rat remembered the conditioned stimulus (CS) and the unconditioned stimulus (US) from the prior trial and those memories along with the CS on the current trial become the signal for the current US. Experiments 2 and 3, which tested hypotheses about instrumental learning, identified why NR different transitions lose their capacity to promote vigorous responding following extensive acquisition training. This is because cues occurring on the rewarded trials of NR different transitions more validly signal reward than other situational cues and thus overshadow them. Finally, some implications of the present findings for understanding the role of NR different transitions in discrimination learning situations were discussed.