Preventing a feature-positive effect in pigeons.

The feature-positive effect (FPE) is a widespread and robust phenomenon in the context of discrimination learning. It refers to the fact that a distinctive feature associated with a stimulus that is reinforced leads to efficient discrimination learning, whereas the same feature associated with the nonreinforced stimulus inhibits discrimination learning. Two experiments with pigeons showed that the FPE also occurs with a simultaneous discrimination paradigm involving brief discrete trials and no intertrial intervals. A pre-training treatment unexpectedly prevented the expression of the FPE in this discrimination task. The pretraining consisted of having pigeons discriminate the feature/nonfeature visual shapes from a plain background disc. Rewarding responses to the shapes, or alternatively to the blank disc, had the same FPE-preventing effect. A reversal of a feature/nonfeature stimulus discrimination led to an analogous erasure of the FPE. The results are discussed in terms of the concurrence or interference between the various associations that the subjects formed on the basis of the different stimulus-reward correlations they experienced in the different phases of the experiments.