Effect of following an excitatory-inhibitory compound with an intermediate reinforcer

Pavlovian-conditioned inhibition training of the form A++, AB- (where ++ is a strong reinforcer and - is nonreinforcement) was conducted in 3 experiments with rats and 1 with pigeons. Then AB+ training was given (in which + is an effective reinforcer that is weaker than ++). The + reinforcer was achieved by reducing the frequency, lessening the amount, or lengthening the delay with which ++ was delivered. All 4 experiments found the AB+ treatment to enhance responding to both the excitatory A and the inhibitory B in comparison with untreated control stimuli. However, when appropriate assessments were made, the increase was more substantial for the inhibitory B. This pattern of results presents challenges for most current theories of associative learning.