A Mathematical Index of Performance on Fixed‐interval Schedules of Reinforcement

On fixed-interval schedules of reinforcement, subjects are reinforced for the first response which occurs after a fixed time interval has elapsed.Responses occurring before the interval has elapsed are recorded, but have no specified consequences.Fixed-interval schedules pro- duce characteristic response patterns.A period without responses (initial pause) occurs at the start of each interval, and is followed by accelerated responding which reaches a con- stant high rate that is maintained until reinforcement.The present paper reports the de- velopment of a mathematical index for describing characteristics of fixed-interval curves.Examples from behavioral and pharmacological studies will illustrate applications of this index. DERIVATION OF THE INDEX OF CURVATURE'A cumulative-response record drawn to approximate the performance of a pigeon trained on a 10-minute, fixed-interval schedule (FI 10) is presented in Fig. 1.If the response rate were constant throughout the interval, the cumulative-response record could be completely described by the straight line O Y.However, the actual cumula- tive record departs from a straight line.Insofar as we can indicate the extent and the SUMMARY A mathematical method for indicating the extent and direction of curvature on cumula- tive records of fixed-interval performances has been developed.This index of curvature is in- dependent of average response rates.The use of the index was illustrated by applying it to the acquisition of fixed-interval performances by squirrel monkeys and to the effects of chlorpromazine on the fixed-interval performances of pigeons.