A comparison of two models for performance under fixed interval schedules of reinforcement

Two models are proposed for responding under fixed-interval schedules of reinforcement. The first model is a Poisson model and seems suitable for situations in which responding produces a classical “FI scallop”. A second model is then developed to describe “break and run” performance, which is also known to occur under some Fixed Interval schedules. The models do not however give any indication of the circumstances under which a particular mode of responding should arise. A comparison of the models to a small set of data collected from rats performing under an FI 60 sec schedule indicates that for the data considered, the second model (a State model) produced by far the best fit.