Fig. 2. Schedule control (timing) is demonstrated by the development of a “scalloped” pattern of responding over the fixed-interval.

A) Hypothetical cumulative response record illustrating how Index of Curvature is calculated. B) Pattern of responding across an FI exhibits a higher IoC at the completion of training (blue circles) when compared to a more linear pattern early in training (grey circles). The accelerating response pattern is characterized by a high density of lever-presses during the final minute of the FI (inset bars). C) Trial response rates decline over the course of training (left; triangles with dotted trace) as function of reduced responding early in the interval. Mean lever-pressing during the last minute of the FI (left; circles with solid trace) does not differ between the first and last training session. Mean index of curvature (Right) increases across training sequence. All training data is shown as group means across training at each schedule (grey symbols), along with final baseline values (right x-axis). Values from the first and last training session demonstrate changes withing training block.