For some years, theorists have believed that the explanation of the PREE and some of the other reward-schedule effects involves common underlying mechanisms, though the nature of the specific mechanisms that have been offered has differed from one theory to another. Our ontogenetic investigations begin to suggest that whereas these earlier explanations may or may not be reasonable for adult rats (and other mammalian species), they may not be entirely satisfactory for the infant to weanling rat. This is particularly clear if we compare the ages of appearance of a number of the reward-schedule effects, presented in the last chapter as Table 7.1.

Do theories based on adult behavior explain the order of appearance of the reward-schedule effects in infants?

According to frustration theory, the PREE, first seen in the 12- to 14-day range, involves a more complex chain of associations than the MREE or SNC, which are seen at successively later ages: The latter two effects involve the emergence of primary frustration as a result of extinction or reduced reward, the subsequent conditioning of anticipatory frustration, and the action of this conditioned frustration to strongly (paradoxically) suppress instrumental responding. In contrast, the PREE involves not only the first three stages – the conditioning of reward expectancy, primary frustration, and the conditioning of frustration – but also a fourth, the counterconditioning of feedback stimulation from anticipatory frustration to instrumental responding.