Qualitative and quantitative considerations in encoding difficulty effects

We hypothesized that the effects of encoding difficulty on the memorability of verbal material would depend on both the type of processing induced by the difficulty manipulation and the type of processing afforded by the material. We predicted that if the processing induced by encoding difficulty were complementary to the processing afforded by the material, then difficulty would enhance recall more so than if the processing induced by the two sources were redundant. These expectations were tested by requiring subjects to process either a structured or an unstructured word list with either a sorting task or a pleasantness rating task; the difficulty of each orienting task was also manipulated. We assumed that sorting and pleasantness rating required primarily relational and individual-item processing, respectively, and that the structured and unstructured word lists afforded relational and individual-item processing, respectively. These assumptions were supported by clustering in free recall and by recognition performance. The primary finding was that difficult sorting increased recall only for the unrelated list, whereas difficult pleasantness judgments increased recall most robustly for the related list. These results support the present framework and help illuminate the boundary conditions of the "difficulty effect."