Stimulus Control After Training with Fixed Interval and Variable Interval Schedules of Reinforcement

Abstract

Rats received discrimination training where light-on was the S+ condition and light-off the S- condition. 2 Ss were trained with a fixed interval (FI) 30-sec. schedule with a limited hold of 5 sec. during S+, while 3 Ss were trained with a variable interval (VI) 30-sec. schedule during S+. Probe testing produced steeper generalization gradients for the FI trained Ss than for the VI trained Ss. Exp. 2 was conducted with 2 more VI Ss trained and tested in an identical manner to the FI Ss of Exp. 1. Gradients for the FI Ss of Exp. 1 were steeper than for those of the VI Ss of Exp. 2. Thus less stimulus control was exerted after training with VI than with FI schedules. The discriminative properties of reinforcement during the VI schedule competed with and thereby weakened S+ stimulus control. An alternate explanation in terms of changes in response patterns was discussed.