Retrieval practice and spacing effects in young and older adults: An examination of the benefits of desirable difficulty

In the present study, we examined how the function relating continued retrieval practice (e.g., one, three, or five tests) and long-term memory retention is modulated by desirable difficulty (R. A. Bjork, 1994). Of particular interest was how retrieval difficulty differed across young and older adults and across manipulations of lag (Exp. 1) and spacing (Exp. 2). To extend on previous studies, the acquisition phase response latency was used as a proxy for retrieval difficulty, and our analysis of final-test performance was conditionalized on acquisition phase retrieval success, to more directly examine the influence of desirable difficulty on retention. The results from Experiment 1 revealed that continued testing in the short-lag condition led to consistent increases in retention, whereas continued testing in the long-lag condition led to increasingly smaller benefits in retention for both age groups. The results from Experiment 2 revealed that repeated spaced testing enhanced retention relative to taking one spaced test, for both age groups; however, repeated massed testing only enhanced retention over taking one test for young adults. Across both experiments, the response latency results were overall consistent with an influence of desirable difficulty on retention. The discussion focuses on the role of desirable difficulty during encoding in producing the benefits of lag, spacing, and testing.