The New Theory of Disuse (NTD): This theoretical framework provides a rationale for why difficulties can be desirable. The NTD characterizes an item in memory by two strengths:
Storage Strength: Represents how well learned and interconnected an item is in memory. The theory assumes that storage strength, once accumulated, is never lost .
Retrieval Strength: Represents the current ease of access to an item given available cues. Retrieval strength is dependent on recency and the association with current cues, and generally declines over time and as contexts change.