Different temporal patterns of memory incorporations into dreams for laboratory and virtual reality experiences: relation to dreamed locus of control

Abstract

Previous work demonstrates that memories about a target experience are incorporated into dream content according to a U-shaped temporal pattern with a peak of incorporations around 1-2 days following the experience (day-residue effect), a diminution on days 3-4, and a recurrence of incorporations on days 5-7 (dream-lag effect). This temporal pattern has been observed for many types of experiences, but no study has yet investigated either whether the pattern occurs differentially for qualitatively distinct, yet temporally proximal, experiences or whether the pattern also manifests by generic changes not specifically related to the target memory. The current study traced memory source incorporation patterns of two qualitatively distinct but temporally overlapping events: a laboratory overnight stay (LAB), considered to be an interpersonal and passive experience; and a virtual reality maze task (VR), considered to be a solitary and active experience. Hypotheses were that: 1) elements of LAB and VR experiences would be incorporated independently and exhibit different temporal patterns of incorporation into dream content; and 2) these incorporation patterns would be associated with different generic changes in dream content, i.e., a primarily external dreamed Locus of Control (Dream LoC) for dreams incorporating LAB experiences and a primarily internal Dream LoC for dreams incorporating VR experiences. Twenty-six participants each spent 1 night in the sleep laboratory, underwent a VR maze task in the morning, and then kept a home dream log for 10 days. Judges rated dreams for evidence of incorporation of LAB and VR experiences. Results were consistent with expectations: 1) LAB and VR experiences showed independent and opposite temporal incorporation patterns; LAB incorporations showed both day-residue and dream-lag effects whereas VR incorporations revealed a peak only on day 4; 2) Dream LoC scores were more external for Day 1 (peak of LAB incorporations), and more internal for Day 4 (peak of VR incorporations). Different incorporation patterns for these two experiences may reflect separate underlying processes of memory consolidation responding to different types of stimulus events. Further, temporal patterning of both specific dream incorporations and general dream content changes (LoC) may reflect qualitatively different aspects of episodic memory consolidation.