Second-order schedules: comparison of different procedures for scheduling paired and nonpaired brief stimuli.

Pigeons performed on a second-order schedule in which fixed-interval components were maintained under a variable-interval schedule. Completion of each fixed-interval component resulted in a brief-stimulus presentation and/or food. The relation of the brief stimulus and food was varied across conditions. Under some conditions, the brief stimulus was never paired with food. Under other conditions, the brief stimulus was paired with food; three different pairing procedures were used: (a) a response produced the simultaneous onset of the stimulus and food; (b) a response produced the stimulus before food with the stimulus remaining on during food presentation; (c) a response produced the stimulus and the offset of the stimulus was simultaneous with the onset of the food cycle. The various pairing and nonpairing operations all produced similar effects on performance. Under all conditions, response rates were positively accelerated within fixed-interval components. Total response rates and Index of Curvature measures were similar across conditions. In one condition, a blackout was paired with food; with this different stimulus in effect, less curvature resulted. The results suggest that pairing of a stimulus is not a necessary condition for within-component patterning under some second-order schedules.