Mechanisms of spaced-trial runway extinction in pigeons

Three experiments with pigeons examined the mechanisms underlying the partial reinforcement extinction effect (PREE), or greater persistence in extinction after training with partial, rather than continuous, reinforcement. All experiments involved runway performance, food reinforcement, and one trial per day. Experiment 1 provided evidence of the PREE together with evidence that large reward increased persistence relative to small reward. Experiment 2 demonstrated that the random mixture of different reward magnitudes increased persistence. Experiment 3 provided evidence that the PREE was not eliminated by chlordiazepoxide (benzodiazepine anxiolytic) but was eliminated by nicotine (cholinergic stimulant) and haloperidol (dopaminergic antagonist). The results are discussed in relation to comparative studies of learning in situations involving surprising reward downshifts.