The Power of Optimal Encoding: Distinctiveness and Differentiation Defeat Directed Forgetting
Hourihan, Kathleen Laura
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The goal of this dissertation is to examine circumstances that encourage optimal encoding in memory. To accomplish this, several encoding manipulations were examined in the context of intentional forgetting. The typically robust item method directed forgetting effect is attributed to selective rehearsal: Participants intentionally select the Remember items as having priority in memory and rehearse them, at the same time choosing not to rehearse Forget items. A series of new experiments demonstrate that when encoding is already optimal, intentional selection processes are ineffective at improving memory further, thus eliminating directed forgetting. These circumstances must serve to promote differentiation of items in a distinctive context. Distinctiveness is defined as a relatively well-remembered set of items standing out against a weaker background set of items. Differentiation refers to individual items being processed in a unique manner such that they stand out against all other items. Only when items are differentiated and in a distinctive context will optimal encoding occur and directed forgetting be eliminated. Experiments 1-3 demonstrated that pictures, imagery, and production are all subject to intentional selection processes when studied alone (i.e., they produce directed forgetting). However, when these differentiated forms of encoding take place in the presence of weaker background items, encoding benefits from both differentiation and distinctiveness, and is optimal—resistant to intentional forgetting. Experiment 4 demonstrated that differentiation in a distinctive context is the key ingredient for eliminating directed forgetting: When encoding is improved with non-unique semantic processing, then item selection processes can still operate, and directed forgetting is produced. Taken together, these experiments show that when differentiated items are studied in a distinctive context, the strong items are not subject to directed forgetting. Yet when these same differentiated items are studied in a non-distinctive context, directed forgetting does occur. Differentiation in the absence of distinctiveness is not sufficient to eliminate directed forgetting, nor is distinctiveness in the absence of differentiation sufficient to eliminate directed forgetting. Both encoding processes must be in place for directed forgetting to be abolished. This pattern provides evidence that optimal encoding can be achieved when differentiation occurs in a distinctive context.