Effects of absolute and relative practice on n-2 repetition costs

Recently, Grange and Juvina (2015) found decreasing n-2 repetition costs with increasing practice. However, in their experiment, no differentiation between absolute and relative strength of the three tasks was possible because all tasks were practiced to the same degree. To further elucidate this issue, two experiments were designed in which for one of the three tasks, aspects of the task set changed during the course of the experiment (Exp. I: Stimulus-response mapping, Exp. II: Cue-task mapping). Replicating Grange and Juvina (2015), decreasing n-2 repetition costs with increasing practice were observed, but the change of stimulus-response mappings in Exp. I did not affect n-2 repetition costs. In Exp. II, n-2 repetition costs were affected by the change of the cue-task-mapping, but no effect of absolute practice was visible. These results suggest that absolute practice influences n-2 repetition costs as long as no change in relative strength is introduced on the level of mapping cues to tasks. If, however, relative task strength is varied, its impact overrides the influence of absolute practice. In addition, the data pattern points towards cue-related instead of response-related inhibitory processes causing n-2 repetition costs.