KINETICS OF MATCHING

Rats responded on concurrent variable interval schedules of brain stim ulation reward in 2-trial sessions. Between trials, there was a 16-fol d reversal in the relative rate of reward. In successive, narrow time windows, the authors compared the ratio of the times spent on the 2 le vers to the ratio of the rewards received. Time-allocation ratios trac ked wide, random fluctuations in the reward ratio. The adjustment to t he midsession reversal in relative rate of reward was largely complete d within 1 interreward interval on the leaner schedule. Both results w ere unaffected by a 16-fold change in the combined rates of reward. Th e large, rapid, scale-invariant shifts in time-allocation ratios that underlie matching behavior imply that the subjective relative rate of reward can be determined by a very few of the most recent interreward intervals and that this estimate can directly determine the ratio of t he expected stay durations.