The relationship between response-reinforcer contingency and instrumental behavior has not been systematically explored.  A longstanding obstacle to the measurement of contingency has been the asymmetry in the definition of the occurrence and nonoccurrence of the response.  This deficiency may be alleviated by defining response and nonresponse uniformly with respect to time.  The proposed experiments investigate the effects of the response (one second occupancy of a target quadrant in an open-field) - reinforcer (intracranial stimulation) contingency on time allocation in the open-field in rats.  In this experiment, the probability of reinforcement given a response and the probability of reinforcement given the absence of a response will be varied across sessions within a subject.  The effects of these variations in the value of contingency will be analyzed with respect to their effect on mean acquisition slope of allocation bias, mean asymptotic allocation bias, and mean activity levels.  More precise specification of the relationship between reinforcement contingency and instrumental time allocation would allow for more rigorous evaluation of contingency models (e.g., learned helplessness hypothesis) and factors which influence contingency-behavior relationships (e.g., pharmacological and physiological interventions).