Non-Interfering Effects of Active Post-Encoding Tasks on Episodic Memory Consolidation in Humans

Abstract

So far, studies that investigated interference effects of post-learning processes on episodic memory consolidation in humans have used tasks involving only complex and meaningful information. Such tasks require reallocation of general or encoding-specific resources away from consolidation-relevant activities. The possibility that interference can be elicited using a task that heavily taxes our limited brain resources, but has low semantic and hippocampal related long-term memory processing demands, has never been tested. We address this question by investigating whether consolidation could persist in parallel with an active, encoding-irrelevant, minimally semantic task, regardless of its high resource demands for cognitive processing. We distinguish the impact of such a task on consolidation based on whether it engages resources that are: (1) general/executive, or (2) specific/overlapping with the encoding modality. Our experiments compared subsequent memory performance across two post-encoding consolidation periods: quiet wakeful rest and a cognitively demanding n-Back task. Across six different experiments (total N = 176), we carefully manipulated the design of the n-Back task to target general or specific resources engaged in the ongoing consolidation process. In contrast to previous studies that employed interference tasks involving conceptual stimuli and complex processing demands, we did not find any differences between n-Back and rest conditions on memory performance at delayed test, using both recall and recognition tests. Our results indicate that: (1) quiet, wakeful rest is not a necessary prerequisite for episodic memory consolidation; and (2) post-encoding cognitive engagement does not interfere with memory consolidation when task-performance has minimal semantic and hippocampally-based episodic memory processing demands. We discuss our findings with reference to resource and reactivation-led interference theories.

The Effect of Post-Learning Wakeful Rest on the Retention of Second Language Learning Material over the Long Term

“…These findings stand in contrast to a number of previous studies investigating the resting effect under different experimental conditions (Brokaw et al 2016;Cowan et al 2004;Craig et al 2014Craig et al , 2015Della Sala et al 2005;Dewar et al 2009Dewar et al , 2012aMercer 2015), but support the results of recent studies, which showed that resting is no prerequisite for successful memory consolidation (e.g. Varma et al 2017). In the following, we address possible arguments for our findings.…”

“…Dewar et al 2007Dewar et al , 2012a. The results of Experiment 1 did not support this view, but showed that post-learning wakeful rest was no prerequisite for successful memory consolidation (see also Varma et al 2017). In Experiment 2, we tested whether the visual distractor task might have modulated our findings in Experiment 1.…”

“…Existing studies implemented different post-learning distractors like spot-thedifference tasks (Dewar et al 2012a), games (Brokaw et al 2016), memorization of words and faces (Mercer 2015), all showing a resting effect. However, only recently, results of a study by Varma et al (2017) showed no beneficial effect of resting. Over six experiments, the authors found similar delayed recall performances in the post-learning rest and distractor condition, even when varying different study parameters like the difficulty of the distractor task.…”

“…However, emerging evidence suggests that resting may not always be associated with beneficial effects in terms of memory retention with relevant studies showing similar memory performances over time in rest and distractor conditions (e.g. Varma et al 2017). In this light, identifying the limits under which resting supports memory retention is essential for its purposed application.…”

“…Studies show that resting can support memory retention (Cowan et al 2004;Della Sala et al 2005;Dewar et al 2012a; for a different view see Varma et al 2017). A brief period of rest after learning new information leads to better delayed recall performances than switching to another task, termed resting effect.…”