Choice in a self-control paradigm: effects of uncertainty

Four experiments examined humans' self-control and impulsiveness as a function of reinforcer uncertainty. Uncertainty was manipulated by varying the probability and durations of interruptions, temporary periods of timeout from reinforcement. In Experiment 1 the probability of an interruption varied while its duration was constant. In Experiment 2 the duration of an interruption varied while its probability was constant. In Experiment 3, the subjects were interrupted only during the delay to the larger, more delayed reinforcer. In Experiment 4 the subjects experienced the same amounts and delays of reinforcement as in Experiments 1-3, but did not experience any interruptions. The subjects in Experiments 1 and 2 were not significantly more impulsive than the subjects in Experiment 4. In Experiment 3, the subjects exhibited significantly more impulsiveness than the subjects in Experiments 1, 2 and 4 when the reinforcement rates were equal, but not when they were unequal. Reinforcer uncertainty affects choice behavior to the extent that it influences the relative reinforcement rate.