The research reported in this article replicated the well-established phenomenon of competition between causes (C) as well as the more controversial presence and absence of competition between effects (E). The test question was identified as a crucial factor leading to each outcome. Competition between causes was obtained when the test question asked about the probability of E given C, p(E/C), implicitly compared with the probability of E given some alternative cause, p(E/C'). competition between effects was obtained when the test question asked about p(C/E) implicitly compared with p(C/E'). Under these conditions, effects competed for diagnostic value just as causes competed for predictive value. Additionally, some conditions in which neither causes nor effects competed were identified. These results suggest a bidirectional and noncompetitive learning process, the contents of which can be used in different ways (competitively or noncompetitively and forward or backward) as a function of test demands.

Two experiments are reported that demonstrate temporal integration of independently acquired temporal relationships, including backward associations, in both human (Experiment 1) and nonhuman (rats, Experiment 2) subjects. The experiments were designed and analyzed in the framework of the temporal coding hypothesis (e.g., Matzel, Held, & Miller, 1988; Savastano & Miller, 1998) as a strategy toward illuminating the use of temporal information and assessing the existence of temporal backward associations. Both experiments provided evidence of retrieval of associations to an event that was expected to occur prior to the moment in time at which a stimulus was presented (i.e., backward associations). In addition, Experiment 1 constitutes the first controlled demonstration of temporal integration by human subjects.

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In 1 experiment with humans and 3 experiments with rats, the authors sought evidence of temporal integration of independently acquired temporal relationships, including forward and backward temporal associations. The experiments were designed and analyzed in the framework of the temporal coding hypothesis (e.g., L. D. Matzel, F. P. Held, & R. R. Miller, 1988; H. I. Savastano & R. R. Miller, 1998) as a strategy toward illuminating the use of forward and backward temporal associations and assessing the directional nature of these temporal associations. The results obtained suggest that the temporal content of learning about paired events involves a single bidirectional association instead of 2 independent unidirectional, forward and backward, associations.

In two conditioned lick suppression experiments with rats, we examined the permanence of the overshadowing effect as a function of the number of compound reinforced training trials. In Experiment 1, robust overshadowing was observed following 4 compound-US pairings but dissipated with 36 pairings. Overshadowing decreased because responding to the overshadowed stimulus increased, not because responding by the control group decreased. This dissipation was stimulus specific and not attributable to a response ceiling. Experiment 2 extended the generality of the effect to a sensory preconditioning design and further demonstrated that overshadowing lost through many compound-US pairings was restored by posttraining extinction of the training context. The results are explicable in terms of the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) under the assumption that the impacts of first-and second-order comparator processes grow differentially as a function of number of trials. STOUT, ARCEDIANO, ESCOBAR, AND MILLER