Responding initiated by pecks on a start key

Four pigeons were exposed to various fixed-interval (FI) 30-s conditions which included a standard FI30-s condition. In all remaining conditions, a red "start" key light began the interval. Completion of various fixed ratios (FR) on the start key lit a green "work" key light. In Experiment 1, one peck on the start key lit the work key light. Mean postreinforcement pause (PRP) lengthened only slightly when the start-key contingency was imposed. In Experiment 2, the start-key requirement ranged from FR 1 to FR 50. As the FR requirement increased, the pause on the work key, called the poststart pause (PSP), decreased for three birds at FR 2 but, for all four birds, the PRP and interreinforcement interval (IRI) did not lengthen until FR 50. These results support the hypothesis that the PRP is a function of the IRI and both are refractory to change, while the PSP is seen as a variable that adjusts to different schedule constraints.