Does sleep protect memories against interference? A failure to replicate

Abstract

Across a broad spectrum of memory tasks, retention is superior following a night of sleep compared to a day of wake. However, this result alone does not clarify whether sleep merely slows the forgetting that would otherwise occur as a result of information processing during wakefulness, or whether sleep actually consolidates memories, protecting them from subsequent retroactive interference. Two influential studies suggested that sleep protects memories against the subsequent retroactive interference that occurs when participants learn new yet overlapping information (interference learning). In these studies, interference learning was much less detrimental to memory following a night of sleep compared to a day of wakefulness, an indication that sleep supports this important aspect of memory consolidation. In the current replication study, we repeated the protocol of and, additionally, we examined the impact of intrinsic motivation on performance in sleep and wake participants. We were unable to replicate the finding that sleep protects memories against retroactive interference, with the detrimental effects of interference learning being essentially the same in wake and sleep participants. We also found that while intrinsic motivation benefitted task acquisition it was not a modulator of sleep-wake differences in memory processing. Although we cannot accept the null hypothesis that sleep has no role to play in reducing the negative impact of interference, the findings draw into question prior evidence for sleep's role in protecting memories against interference. Moreover, the current study highlights the importance of replicating key findings in the study of sleep's impact on memory processing before drawing strong conclusions that set the direction of future research.

Fig 1. Study timeline and protocol.

The top part shows the timeline for the Sleep and Wake participants from training to retest. The bottom part describes the word pairs training and retest protocol.

Fig 2. Paired associates results.

Results from Ellenbogen et al. (2009) (Left) are compared to findings from the current study (Right). Results for “no interference” represent recall from the initial retest, prior to interference learning. “Interference” results represent recall of originally-learned B words following interference learning.

Fig 3. Effect size comparison.

Points represent the size of the Sleep x Interference interaction effect as reported by Ellenbogen et al. (2009), and in the current study (partial eta squared). Error bars represent the 90% confidence interval on this effect. The Ellenbogen et al. 2009 effect falls well outside the 90% confidence interval of the current, more precise effect size estimate.