The two-test strategy in the study of inhibitory conditioning.

It is commonly believed that both a summation test and a retardation test should be used to determine whether a stimulus becomes inhibitory in consequence of some specified treatment, because the 2 tests together rule out alternative interpretations. Depending, however, on the choice of control treatments, a single test may provide credible evidence of inhibition or both together may not. A comprehensive review of the 2-test literature shows that suitable controls have been used only rarely and that compelling evidence of inhibition is correspondingly rare. The only such evidence now available is provided by retardation tests in experiments with some variation of A+/AB- training as the putatively inhibitory treatment.