Each reinforcement outcome, we suggest, produces a characteristic memory. For example, a 10 pellet reinforcement produces the memory S10, a 2 pellet reinforcement the memory S2, nonreinforcement the memory SN, and so on. As previously suggested (e.g., Capaldi, 1967), larger reinforcement outcomes give rise to greater excitatory growth, i.e., a 10 pellet reinforcement produces greater excitatory growth than a 2 pellet reinforcement, which in turn produces greater excitatory growth than a 0 pellet reinforcement (or nonreinforcement), which fails to produce excitation. Excitation increases when the excitatory strength acquired by a memory lies below the maximum excitatory strength
supported by a reinforcement outcome. The smaller this discrepancy the smaller the increment in excitatory growth. Inhibition increases when the excitatory strength of a memory exceeds the maximum excitatory strength supported by a reinforcement outcome. The greater the discrepancy the greater the increment in inhibitory growth.