Dissociating neural markers of stimulus memorability and subjective recognition during episodic retrieval

Wilma A Bainbridge,Jesse Rissman

doi:10.1038/s41598-018-26467-5

Abstract

While much of memory research takes an observer-centric focus looking at participant performance, recent work has pinpointed important item-centric effects on memory, or how intrinsically memorable a given stimulus is. However, little is known about the neural correlates of memorability during memory retrieval, or how such correlates relate to subjective memory behavior. Here, stimuli and blood-oxygen-level dependent data from a prior functional magnetic resonance imaging (fMRI) study were reanalyzed using a memorability-based framework. In that study, sixteen participants studied 200 novel face images and were scanned while making recognition memory judgments on those faces, interspersed with 200 unstudied faces. In the current investigation, memorability scores for those stimuli were obtained through an online crowd-sourced (N = 740) continuous recognition test that measured each image’s corrected recognition rate. Representational similarity analyses were conducted across the brain to identify regions wherein neural pattern similarity tracked item-specific effects (stimulus memorability) versus observer-specific effects (individual memory performance). We find two non-overlapping sets of regions, with memorability-related information predominantly represented within ventral and medial temporal regions and memory retrieval outcome-related information within fronto-parietal regions. These memorability-based effects persist regardless of image history, implying that coding of stimulus memorability may be a continuous and automatic perceptual process.

Highlights

Why do we often remember events that are not important to us, yet we forget the faces of acquaintances we desperately try to remember? Much of memory research focuses on answering this question through an observer-centric focus, exploring the steps the brain undergoes when forming a memory and trying to explain the factors that lead some subjects to perform better than others
We used the group-level Amazon Mechanical Turk (AMT) data to calculate a hit rate (HR; percentage of participants successfully identifying a repeat) and a false alarm rate (FA; percentage of participants falsely identifying the first presentation as a repeat)
For the ventral visual stream, we looked at early visual cortex (EVC), and higher-level commonly category-specific perceptual regions of the fusiform face area (FFA), parahippocampal place area (PPA), and lateral occipital complex (LOC)

Summary

Introduction

Why do we often remember events that are not important to us, yet we forget the faces of acquaintances we desperately try to remember? Much of memory research focuses on answering this question through an observer-centric focus, exploring the steps the brain undergoes when forming a memory and trying to explain the factors that lead some subjects to perform better than others. We find that we are able to significantly classify whether individual face stimuli have high or low memorability based on the BOLD data, and the regions supporting this classification significantly differ from regions able to classify memory behavior We find these memorability-related patterns remain relatively consistent across both trials where participants successfully recognized old images (hits) and successfully rejected new images (correct rejections). We find that support vector regressions trained on activity patterns from these same regions are able to predict the memorability score of individual faces, providing the first evidence for a continuous representation of memorability in the brain Taken together, these results provide support for memorability as a measurable stimulus property that can be used to analyze neural correlates of memory, and provide new insights into the information that may be relevant to the brain when retrieving an item from memory

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Results

Conclusion