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"A theory of retrieval difficulty proposed by Bjork and Bjork (1992). They argued that information in memory might be characterized in terms of two strengths:
storage strength,
which refers to a permanent property of the information that determines long-term retention, and
retrieval strength,
which refers to the momentary accessibility of the information.
In their theory , increments in retrieval strength are negatively correlated with increments in storage strength. That is, when retrieval strength is high and information is easily accessible, the retrieval of that information produces small increments in storage strength. In contrast, lower retrieval strength and more difficult retrieval produce greater increments in storage strength and thereby promote long-term retention, assuming the item can be retrieved.
A. Healy, S. Kosslyn, & R. Shiffrin (Eds.), From learning processes to cognitive processes: Essays in honor of William K. Estes (Vol. 2, pp. 35–67). Hillsdale, NJ: Erlbaum. https://pages.wustl.edu/files/pages/imce/memory/2008_agarwal.pdf and Bjork, R. A., & Bjork, E. L. (1992). A new theory of disuse and an old theory of stimulus fluctuation. https://bjorklab.psych.ucla.edu/wp-content/uploads/sites/13/2016/07/RBjork_EBjork_1992.pdf
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