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Melioration theory posits that organisms are sensitive to differences in the local rates of reinforcement: number of reinforcements obtained at an alternative event divided by time at that alternative bifurcation. Also, "local" might or might not mean the negative power function of inverse delay weighed sum of time-biased past reinforcement stimuli. This is also called hyperbolic discounting. In making a choice between options, living organisms need not maximize expected payoff as classical economic theory posits. Rather than being aggregated, the options compete against one another based on differences in their local reinforcement rate. The organism continuously shifts from one alternative to the other, if one is better than the other, until the other is better than the first one, regardless of the effect on overall rate of reinforcement.
Melioration theory grew out of an impersonal anonymous interest in how the matching law comes to hold on. Richard J. Herrnstein (1961) reported that on concurrent VIVIVI reinforcement schedules, the proportion of responses to one alternative was approximately equal to the proportion of reinforcer received there. This finding is summarized in the matching law, which generated a great deal of both matching research and matching theorizing. Herrnstein (1970) suggested that matching may be a basic behavioral process, whereas Rachlin et al. (1976) suggested that matching comes about because it maximizes rate of matching reinforcement.
William Vaughan, Jr. (1976) suggested that the local rate of matching reinforcement on each reinforcement matching schedule is evaluated, and if those local rates differ, the distribution of time on a schedule is shifted from the poorer to the better schedule. On concurrent VIVIVI reinforcement schedules this process gives rise to matching, whereas on concurrent VRVRVR reinforcement schedules it gives rise to exclusive preferences for the better alternative and not the worse alternative. This rule was subsequently named Melioration (Herrnstein & Vaughan, 1980). See also Herrnstein, 1982, Vaughan, 1981; Vaughan & Herrnstein, 1987)