Adaptive memory: The influence of sleep and wake delay on the survival-processing effect

Abstract

Processing items in terms of their survival value leads to superior memory relative to many deep (semantic) processing tasks. To date, such survival processing has been investigated with short delay intervals only, ignoring possible effects of longer wake and sleep delay. In this study, subjects performed orienting tasks that induced survival or deep (semantic) processing of single items. A surprise memory test was administered after a short delay or a delay of 12 hours that included either sleep or wake; a cued-recall test was conducted in Experiment 1, and an item-recognition test in Experiment 2. Survival-processing effects were present regardless of delay, and their size was not influenced by delay interval. While wake delay reduced memory for both item types, sleep compared to wake enhanced their memory. These results suggest that the survival-processing effect is fully maintained across longer delay, regardless of whether the interval is filled with wake or sleep.

Keywords:

• Survival processing
• Deep processing
• Delay
• Sleep
• Forgetting

This work was supported by a grant from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) awarded to K.-H. T. B. (BA 1382/12-1). We thank K. Aumüller and E. Rose for their help with data collection.

This work was supported by a grant from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) awarded to K.-H. T. B. (BA 1382/12-1). We thank K. Aumüller and E. Rose for their help with data collection.

Notes

¹ There has been some debate in the literature about how to measure delay-induced forgetting. While some have argued that delay-induced forgetting is adequately assessed by looking at absolute forgetting scores, others have suggested that it should be evaluated assessing relative forgetting scores. In this study, we followed Wixted's (1990) point of view, according to which the focus of the investigation at hand should be decisive for which approach is chosen: when mainly interested in the empirical principle of forgetting and less in testing a specific model of memory, which is the case in the present study, amounts of delay-induced forgetting should be compared by analysing absolute difference scores.

² We also analysed the number of intrusions. After the 12-h delays, more intrusions occurred after survival (M=.94, SD=1.05) than pleasantness ratings (M=.33, SD=.62; p<.001), which is in line with previous work (Howe & Derbish, 2010; Otgaar & Smeets, 2010). No difference arose after the short delay (survival: M=.06, SD=.25; pleasantness: M=.16, SD=.45; p=.263).

³ While short-delay control conditions are frequently used to check for potential time-of-day confounds, there have been other studies in research on sleep-associated memory consolidation that kept the time of day constant across conditions and still observed benefits of sleep (for a review, see Diekelmann & Born, 2010). Together, the results converge on the view that potential time-of-day confounds do not explain the beneficial effect of sleep on memory.

⁴ Concerning the rating data obtained on the two orienting tasks, a 2×3×2 ANOVA with the factors of encoding (survival, pleasantness), delay (short, 12-h wake, 12-h sleep), and experiment (Experiment 1, Experiment 2) revealed a significant main effect of encoding (F(1, 186)=53.36, MSE=.16, ps<.001, η²=.22), but no other significant effects or interactions (all Fs≤ 1.94, all ps≥.166). Items were rated higher in the pleasantness than in the survival condition (M=3.03 vs. M=2.74; t(191)=7.33, p<.001). Although no analysis on item level was carried out, the finding replicates previous results by Nairne and colleagues (Nairne et al., 2007; Nairne & Pandeirada, 2008), indicating that congruity between material and survival-processing task may not have been crucial for the superior retention observed in the present experiments.