SELF-STIMULATING RATS COMBINE SUBJECTIVE REWARD MAGNITUDE AND SUBJECTIVE REWARD RATE MULTIPLICATIVELY

For rats that bar pressed for intracranial electrical stimulation in a 2-lever matching paradigm with concurrent variable interval schedules of reward, the authors found that the time allocation ratio is based on a multiplicative combination of the ratio of subjective reward magn itudes and the ratio of the rates of reward. Multiplicative combining was observed in a range covering approximately 2 orders of magnitude i n the ratio of the rates of reward (from about 1:10 to 10:1) and an or der of magnitude change in the size of rewards. After determining the relation between the pulse frequency of stimulation and subjective rew ard magnitude, the authors were able to predict from knowledge of the subjective magnitudes of the rewards and the obtained relative rates o f reward the subject's time allocation ratio over a range in which it varied by more than 3 orders of magnitude.