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Participants studied sentences describing two different characters and then were told to forget the sentences about only one of the characters. A second list contained sentences attributed to a third character. Subsequently, they received a recall test on the sentences about the original two characters. When the sentences could be thematically integrated, participants showed no directed forgetting relative to a control group that was never told to forget. However, with unrelated sentences, participants selectively forgot the target character's sentences without forgetting the other character's sentences. This selective directed forgetting effect is a novel empirical result. We interpret the results as consistent with Radvansky's (1999) ideas about inhibition with textual materials.

If strategy shifts speed up performance, learning curves should show discontinuities where such shifts occur. Relatively smooth curves appear consistently in the literature, however. To explore this incongruity, we examined learning when multiple strategies were used. We plotted power law learning curves for aggregated data from four mental arithmetic experiments and then plotted similar curves separately for each participant and strategy. We then evaluated the fits achieved by each group of curves. In all four experiments, plotting separately by strategy produced significantly better fits to individual participants' data than did plotting a single power function. We conclude that improvement of solution time is better explained by practice on a strategy than by practice on a task, and that careful assessment of trial-by-trial changes in strategy can improve understanding of the effects of practice on learning.