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This study focused on variables that may account for response-rate differences under variable-ratio (VR) and variable-interval (VI) schedules of reinforcement. Four rats were exposed to VR, VI, tandem VI differential-reinforcement-of-high-rate, regulated-probability-interval, and negative-feedback schedules of reinforcement that provided the same rate of reinforcement. Response rates were higher under the VR schedule than the VI schedule, and the rates on all other schedules approximated those under the VR schedule. The median reinforced interresponse time (IRT) under the VI schedule was longer than for the other schedules. Thus, differences in reinforced IRTs correlated with differences in response rate, an outcome suggestive of the molecular control of response rate. This conclusion was complemented by the additional finding that the differences in molar reinforcement-feedback functions had little discernible impact on responding.

Eight rats responded on concurrent Variable-Ratio 20 Extinction schedules for food reinforcement. The assignment of variable-ratio reinforcement to a left or right lever varied randomly following each reinforcer, and was cued by illumination of a stimulus light above that lever. Postreinforcement preference levels decreased substantially and reliably over time when the lever that just delivered reinforcement was now in extinction; however, if that lever was once again associated with variable ratio, this decrease in same-lever preference tended to be small, and for some subjects, not in evidence. The changes in preference level to the extinction lever were well described by a modified version of Killeen, Hanson, and Osborne's (1978) induction model. Consistent with this model's attribution of preference change to induction, we attribute preference change in this report to a brief period of reinforcer-induced arousal that energizes responding to the lever that delivered the last reinforcer. After a few seconds, this induced responding diminishes, and the operant responding that remains comes under the control of the stimulus light cuing the lever providing variable-ratio reinforcement.

382Many operant accounts of behavioral output and choice can be classified in terms of whether reinforcement is thought to affect behavior at a molecular level, such as the time between two responses (interresponse time, or IRT) or the order in which choices occur, or at a more molar level, such as the relation between reinforcement rate and the rate of response emission or the frequency with which choices occur. Theorists who have applied molecular or molar models to single and concurrent operants have tended to favor the same type of account, be it molar or molecular, for both operant tasks. For example, Shimp (1966Shimp ( , 1973 and Herrnstein (1970) have advanced molecular and molar levels of analysis, respectively, to accommodate single-and choice-schedule performances.Although it seems unsurprising that theorists favor a single level of analysis in modeling single-and concurrentschedule effects, nothing besides parsimony forces this approach. Indeed, the present report entertains the possibility that control by reinforcement may differ in its level of action in single versus concurrent schedules. Our review of extant findings supports the view that behavioral sensitivity to reinforcement is best explained molecularly for single operants, but in a molar fashion for concurrent operants. Evidence Supporting Molecular Accounts of Single-Schedule PerformanceTanno and Sakagami (2008; see also Peele, Casey, & Silberberg, 1984) have suggested that the response rate difference between variable ratio (VR) and variable interval (VI) schedules with equated reinforcer rates may be largely attributable to a molecular factor: On VI schedules, the probability of reinforcement grows with time between successive responses, but on VR schedules, it does not. This between-schedule difference may account for the lower response rates VI schedules support.Tanno and Sakagami (2008) made their case by comparing response rates on a VR schedule with those maintained by other schedule types that were purpose-built to alter the molar relationship between response rate and reinforcement rate. Although their between-schedule comparisons permitted the emergence of molar control over response rate (i.e., on the basis of the feedback relation between response rate and reinforcement rate), it did not appear. Instead, the sole factor that seemed responsible for rate differences between VR and all comparison schedules was differences in the reinforced IRT distributions. They interpreted this result as establishing the primacy of a molecular account of the VR-VI rate difference based on between- AND TAKAYUKI SAKAGAMIKeio University, Tokyo, JapanIn the first condition in Experiment 1, 6 rats were exposed to concurrent variable ratio (VR) 30, variable interval (VI) 30-sec schedules. In the next two conditions, the subjects were exposed to concurrent VI VI schedules and concurrent tandem VI-differential-reinforcement-of-high-rate VI schedules. For the latter conditions, the overall and relative reinforcer rates equaled those in the first conditio...

Resurgence is the recurrence of a previously reinforced and then extinguished response when a more recently reinforced response is extinguished. The purpose of the present experiments was to examine the relation between alternative reinforcement rates and resurgence with pigeons. Each experiment consisted of a three-phase procedure and each phase of three experiments was a two-component multiple schedule, except for Experiments 2a and 2b, which employed single schedules. In each experiment, the target response was reinforced according to a variable-interval (VI) schedule in the Acquisition phase. In the Elimination phase, the target response was eliminated using either extinction or a differential-reinforcement-of-other-behavior (DRO) schedule and the alternative response was reinforced according to a VI schedule. The rate of alternative reinforcement differed between components, but the number of reinforcers per hour (and thus the reinforcement ratio) was 60 and 180 in the Lean and Rich