Preference pulses are defined as a tendency in choice for relative response rate to decline with time since receipt of the just-reinforced alternative. McLean, Grace, Pitts, and Hughes (2014) suggested preference pulses may not be solely a local reinforcement effect, but rather may include an artifact due to run structure of responding. If so, pulses after reinforcement should also appear if reinforcement is omitted. To evaluate whether occasional reinforcer omission leaves run structure unaffected, seven food-deprived rats responded for food pellets on a two-component multiple schedule of concurrent schedules. In both components, the assignment of reinforcement to a left or right lever varied randomly following each reinforcer. One of the components was a concurrent Variable-Interval (VI) 30-s Extinction (EXT) schedule. A stimulus light above the lever identified its association with the VI schedule. The second component was a concurrent VI 30-s VI 30-s schedule. In this component, the stimulus light above each lever was illuminated, and reinforcement was sometimes omitted randomly after the VI requirement was met. In the first component, preference pulses were reliably observed after reinforcement and its omission when the just-reinforced lever was the now-EXT lever ; however, when the just-reinforced lever was the VI lever again, and its next reinforcer was omitted, pulsing was not in evidence. Instead, an "antipulse" : a tendency for relative response rate to increase to the just-omitted lever, obtained. Additional analyses showed the initial choices after reinforcer omission were (1) more variable than the choices thereafter, (2) more variable than the first several choices after reinforcement, and (3) faster than the choices thereafter. These features suggest the manipulation of reinforcer omission has specific effects on choices that follow, resulting in the occurrence of preference pulses to the EXT lever and antipulses to the VI lever.
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