Storage Strength and Retrieval Strength

The New Theory of Disuse, developed by Robert A. Bjork and Elizabeth Ligon Bjork, proposes that every memory trace possesses two independent dimensions of strength. Storage strength captures how well information has been encoded—the depth, richness, and connectivity of the trace within the broader knowledge network. It accumulates across repeated exposures and never decreases; even forgotten information retains its storage strength. Retrieval strength captures how easily information can be accessed right now—the current activation level that determines fluency of recall. Unlike storage, retrieval strength fluctuates constantly, rising with recent use and falling with disuse. The critical finding: the two strengths respond differently to learning conditions and are often inversely related. Massed practice builds high retrieval strength (the material feels accessible) and low storage strength (shallow encoding). Spaced practice builds low retrieval strength during gaps (material feels less accessible) but high storage strength through effortful retrieval across those gaps.