Intentional forgetting is easier after two "shots" than one.

Three experiments evaluated whether the magnitude of the list-method directed forgetting effect is strength dependent. Throughout these studies, items were strengthened via operations thought to increase context strength (spaced presentations) or manipulations thought to increment the item strength without affecting the context strength (processing time and processing depth). The assumptions regarding which operations enhance item and context strength were based on the "one-shot" hypothesis of context storage (K. J. Malmberg & R. M. Shiffrin, 2005). The results revealed greater directed forgetting of strong items compared with weak items, but only when strength was varied via spaced presentations (Experiment 3). Equivalent directed forgetting was observed for strong and weak items when strengthening operations increased item strength without affecting the context strength (Experiments 1 and 2). These results supported the context hypothesis of directed forgetting (L. Sahakyan & C. M. Kelley, 2002).