These experiments compare the effects of delayed Judgment of learning and Retrieval practice on recall, both to evaluate the impact of the former and to evaluate potential mechanisms.
Broadly, their experiments found inconsistent evidence suggesting that delayed judgments of learning (with cue only) improve recall over restudy; and relatively reliable evidence showing that retrieval practice has a more substantial effect.
One mechanism proposed for delayed JOLs is the “{covert retrieval hypothesis},” which suggests that delayed JOLs improve recall because they {evoke Implicit retrieval practice}. This hypothesis can’t fully explain the data, since {overt retrieval fared better than delayed JOLs}.
The data better supports the “{truncated search hypothesis},” which suggests that {delayed JOLs are like a less effortful retrieval practice in which people stop searching before retrieving the full answer}.
But in fact it seems that people perform both covert retrieval and truncated search, and the data supports a previous hypothesis (Son and Metcalfe, 2005) that when people judge that a cue is unfamiliar, they truncate their search, but when it’s familiar, they attempt retrieval.