Retrieval learning practice

Jeffrey Karpicke and Janell Blunt published on Science express a report about their research on retrieval practice in learning.
Karpicke studied the subject just in 2008 with Roediger III in The critical importance of retrieval for learning. Here and in the successful paper he confrounts retrieval with elaborative studying. Just in the 2008 paper he writes

repeated testing produced a large positive effect

But what is retrieval?
I found on Purdue the following definition:

Retrieval is a process of recalling what we have in memory.

So retrieval practice is the practice used by students to recall informations. In this vision I think that retrieval and elaborative studying are not so different in principle in the use of our brain, but, according to Karpicke and Blunt's results, retrieval is probably more useful for exams and elaborative is more useful if you want obtain more persistence results.
Karpicke and Blunt performed two experiments. In the first test 80 Purdue University undergraduate students studied on Sea Otters. Students are divided in 4 groups: study, repeated study, concept mapping, retrieval practice.
In data elaboration researchers pay attention in different learning activities: they can depend on the strucuture of the materials.
The conclusions:

Research on retrieval practice suggests a view of how the human mind works that differs from everyday intuitions. Retrieval is not merely a read out of the knowledge stored in one's mind – the act of reconstructing knowledge itself enhances learning. This dynamic perspective on the human mind can pave the way for the design of new educational activities based on consideration of retrieval processes.

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