On the primacy of molecular processes in determining response rates under variable-ratio and variable-interval schedules

Abstract

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.

Fig 1

Reinforcers per min as a function of responses per min presented as molar feedback functions. The top two panels present the feedback function for VR (left panel) and the determination of a specific reinforcer rate at a given response rate (right panel). The bottom panels present the feedback function for the RPI (left panel) and NF (right panel) schedules. The symbols R_VR and B_VR that appear represent values of the variables in Equations 1 and 2.

Fig 2

Reinforcers per min as a function of responses per min in the eight experimental conditions. See text for additional details.

Fig 3

Responses per min for the different schedule types for each rat. Multiple points appear where the schedule was reintroduced. The bars show the standard deviation from the last five sessions in each condition.