Multiple-object Tracking as a Tool for Parametrically Modulating Memory Reactivation

Abstract

Converging evidence supports the “non-monotonic plasticity” hypothesis that although complete retrieval may strengthen memories, partial retrieval weakens them. Yet, the classic experimental paradigms used to study effects of partial retrieval are not ideally suited to doing so, because they lack the parametric control needed to ensure that the memory is activated to the appropriate degree (i.e., that there is some retrieval, but not enough to cause memory strengthening). Here we present a novel procedure designed to accommodate this need. After participants learned a list of word-scene associates, they completed a cued mental visualization task that was combined with a multiple-object tracking (MOT) procedure, which we selected for its ability to interfere with mental visualization in a parametrically adjustable way (by varying the number of MOT targets). We also used fMRI data to successfully train an “associative recall” classifier for use in this task: this classifier revealed greater memory reactivation during trials in which associative memories were cued while participants tracked one, rather than five MOT targets. However, the classifier was insensitive to task difficulty when recall was not taking place, suggesting it had indeed tracked memory reactivation rather than task difficulty per se. Consistent with the classifier findings, participants’ introspective ratings of visualization vividness were modulated by MOT task difficulty. In addition, we observed reduced classifier output and slowing of responses in a post-reactivation memory test, consistent with the hypothesis that partial reactivation, induced by MOT, weakened memory. These results serve as a “proof of concept” that MOT can be used to parametrically modulate memory retrieval – a property that may prove useful in future investigation of partial retrieval effects, e.g., in closed-loop experiments.

A Study of the Brain Network Connectivity in Visual‐Word Pairing Associative Learning and Episodic Memory Reactivating Task

“…The fMRI data used in this study were obtained from the OpenfMRI database [ 17 , 20 ]. The accession number of the data is ds002311, and the data are freely available at https://openfmri.org/data-set/ds002311/ .…”

“…The original fMRI data set contains 23 right-handed T1 structural image data and four sets of functional image data [ 17 ]. The data of 8 of subjects was corrupted, so the data of the remaining 15 people were used.…”

“…For example, in the case of think/no-think paradigm, the relationship between the differences in conditions and memory basically corresponds to the fact that there is no change in memory in the case of extremely low activation, while memory is weak in the case of moderate activation and enhanced in the case of high activation [ 16 ]. In the task with multiple-object tracking interference, subjects need to continuously track some moving target points during a period of time, while visualizing the scene associated with the words appearing in the center of the screen [ 17 ]. In this task, subjects need to be highly focused while tracking the targets; otherwise, the task will be difficult to complete successfully [ 15 ].…”