Adaptation to conflict frequency without contingency and temporal learning: Evidence from the picture-word interference task

In interference tasks (e.g., Stroop, 1935), the difference between congruent and incongruent latencies (i.e., the "congruency" effect) is larger in trial blocks containing mostly congruent trials than in trial blocks containing mostly incongruent trials (the proportion-congruent [PC] effect). Although the PC effect has typically been interpreted as reflecting adjustments in attention toward/away from the task-irrelevant dimension (i.e., a conflict-adaptation strategy), recent research has suggested alternative accounts based on the learning of either contingencies (i.e., distractor-response associations) or of temporal expectancies (i.e., the typical response speed on previous trials), accounts in which conflict adaptation plays no role. Using the picture-word interference paradigm, we report data from two PC manipulations in which contingency learning was made impossible by using nonrepeated distractors (Experiment 1A) or both nonrepeated distractors and responses (Experiment 1B). The classic PC effect emerged in both experiments. In addition, learning of temporal expectancies could not explain the present PC effects either, as results from trial-level analyses of Experiments 1A and 1B and a nonconflict version of Experiment 1B (Experiment 2) were inconsistent with the predictions of the temporal learning account of PC effects. These results suggest that conflict adaptation remains a credible explanation for PC effects.