Storage Strength vs. Retrieval Strength

Storage strength and retrieval strength are the two dimensions every memory trace possesses in Bjork and Bjork's 1992 framework. Storage strength reflects the item's integration into long-term memory—its richness of encoding, its connections to other knowledge, its resistance to interference. Retrieval strength reflects the item's current accessibility—how likely it is to come to mind when needed right now. The two are independent: a deeply stored item can have low retrieval strength (a childhood friend's name you struggle to recall), and a shallowly stored item can have high retrieval strength (a phone number you just looked up). The independence resolves the paradox of desirable difficulties: spacing, generation, and interleaving reduce current retrieval strength (making practice feel harder) while building storage strength (making retention stronger). AI maintains external retrieval strength permanently—users always have access—preventing the drop in retrieval strength that triggers the effortful re-retrieval that builds storage strength.