Stimulus control of temporally spaced responding in second-order schedules.

Second-order schedules consisting of sequences of component differential-reinforcement-of-low-rate schedules were used to investigate two different methods of introducing exteroceptive stimuli. When different exteroceptive stimuli were associated with each component (chained schedule), periods of pausing and lower response rates developed in the early components compared to the early components of the same sequence in the presence of a single exteroceptive stimulus (tandem schedule). When a brief stimulus change occurred at the completion of each component, response rates were higher in the early components compared to the tandem schedule. Changes in response rates in the early components were directly related to changes in reinforcement frequency in the terminal components produced by the two methods of presenting the exteroceptive stimuli.