A reanalysis of cue -competition effects in Pavlovian fear conditioning in rats: Implications for neuronal theories of learning and memory

In a set of 7 experiments, the author examined if cue-competition effects such as blocking and overshadowing reflect deficits in learning (e.g., Rescorla & Wagner, 1972) or deficits in performance (Miller & Schachtman, 1985). To this end, the author tested if the ability of a blocked and/or overshadowed stimulus was weakened in its ability to serve as a blocker or second-order reinforcer for a novel stimulus. It was assumed that the ability of a stimulus to serve as a blocker or second-order reinforcer depended on its associative status, and not on the performance it evoked. CS-evoked suppression of appetitively-motivated barpressing served as the dependent measure of conditioned performance. Experiment 1 found that an overshadowed CS was weakened in its ability to serve as a blocker. Experiment 2 replicated Experiment 1 and further showed that a blocked stimulus was also weakened in its ability to serve as a blocker. Experiment 3 showed that a blocked and overshadowed stimulus was weakened in its ability to serve as a second-order reinforcer. The results of Experiments 1, 2, and 3 were construed as supporting a learning-deficit as opposed to a performance-deficit interpretation of cue-competition effects. Performance-deficit theorists, however, might claim that the weakened ability of a blocked and/or overshadowed CS to serve as a blocker or second-order reinforcer was due to the presence of an intact A-US association (the association produced by the blocking and/or overshadowing CS). Experiments 4 to 7 addressed this issue, using various techniques, which might weaken the allegedly interfering A-US association. Experiments 4 and 5 showed that extinguishing the blocking and/or overshadowing stimulus did not facilitate performance to and blocking ability of a blocked and/or overshadowed stimulus (Experiment 4) or overshadowed stimulus (Experiment 5). Experiment 6 further showed that subjecting the blocking and/or overshadowing cue to a Pavlovian conditioned inhibition procedure also did not enhance performance to the blocked and/or overshadowed stimulus. Finally, Experiment 7 showed that extinguishing the overshadowing stimulus weakened performance to the overshadowed stimulus. Collectively, the results of Experiments 1 to 7 are consistent with learning-deficit interpretations of cue-competition effects (e.g., Rescorla & Wagner, 1972; Mackintosh, 1975)