ABSTRACT
Of the many contributions that Bob Bjork has made to the eld of memory research, the concept of desirable diculties in learning is arguably one of the most provocative and far reaching in terms of its potential impact on training and educational practices. In a series of papers during the early 1990s (Bjork, 1994a, 1994b; Christina & Bjork, 1991; Schmidt & Bjork, 1992), Bjork challenged the commonly held belief that factors that enhance performance or speed improvement during learning also produce superior long-term retention and transfer. Reviving the neglected distinction between the momentary strength of a response and the enduring habit strength of that response (e.g., Estes, 1955; Guthrie, 1952; Hull, 1943; Skinner, 1938; Tolman, 1932), he argued that performance during learning reects momentary accessibility of knowledge or skill rather than its underlying storage strength. us, performance during learning can be a poor indicator of whether that knowledge or skill will be accessible (or available) in the future. Based on this line of reasoning and a review of the relevant literature, Bjork reached a seemingly contradictory conclusion: Introducing diculties during learning can actually increase long-term retention and transfer.
