Preference for sequences of rewards: further tests of a parallel discounting model.

Brunner and Gibbon [Brunner, D., Gibbon, J., 1995. Anim. Behav. 50, 1627-1634] studied rats' choices between sequences of equal numbers of rewards that differed in their temporal arrangement. Rats' preferences were well accounted for by a parallel discounting model of aggregate food value in which the sequence value is the simple sum of the hyperbolically discounted value of the individual rewards [Mazur, J.E., 1984. J. Exp. Anal. Behav. 46, 67-77]. Three experiments reported here extend their work to sequences of unequal number of rewards and test the specific prediction that rats prefer sequences that get worse with time over sequences that improve, given that the total reward rate is the same. Choice functions from this and other two experiments that offered choice between unequal reward numbers were S-shaped and supported a signal detection-like model in which the value of each option obeys the parallel discounting model.