The present experiments evaluated whether transitions in reinforcer probability are necessary to induce attack in pigeons. In Experiment I, three of six pigeons exposed to response-contingent constant-probability food schedules and a photograph of a conspecific as a target exhibited sustained postreinforcement attack on the target. The postreinforcement pattern of attack developed over the course of the experiment and was accompanied by a reduction in the rate of postreinforcement key pecking and an increase in the postreinforcement pause in key pecking. These effects on key pecking resulted in unprogrammed variations in the probability of reinforcement which may have been responsible for the induction of attack. In Experiment II, the attack-inducing properties of a constant-probability response-independent food schedule were compared to a periodic food schedule matched for overall rate of food delivery and to a no-food condition. In addition to attack, the spatial location of the subjects was monitored during each interfood interval. The periodic and aperiodic food schedules generated very different patterns of spatial location. Postfood attack was induced by both food schedules, although the constant-probability schedule induced attack in fewer birds. The no-food condition was not effective in inducing attack in any birds. These experiments indicate that intermittent food schedules without reductions in reinforcer probability are sufficient to induce attack in some pigeons, although not as effective as schedules with transitions in reinforcer probability.
