Oscillatory correlates of free-recall dynamics due to perceptual shifts

Abstract

The human memory system interacts with an ever-changing perceptual environment, and the perceptual properties of new information can shape that information’s mnemonic fate. Experimentally, shifts in perception to a salient stimulus have been shown to enhance memorability of post-shift items (Murdock and Walker, 1969). Despite this work, the neural signals that reflect this enhanced memorability at perceptual boundaries remain to be characterized. Sederberg et al. (2006) described global shifts in the oscillatory topography elicited by studied items at early vs. late serial positions, and showed distinct subsequent memory responses for items of each type. In a scalp EEG experiment, we expanded on these findings by manipulating the presentation modality (auditory vs. visual) of studied material to elicit a mid-list perceptual shift that enhances the memorability of the post-shift item. These post-shift items elicited an oscillatory response which showed enhanced delta activity (2-4 Hz) and diminished alpha activity (10-14 Hz) relative to non-shift items from the same modality. We contrast these effects with the list position effects described by Sederberg et al. (2006), with an aim to further inform our understanding of the processes underlying the effects of contextual shifts on episodic memory.