Poppenk Jordan, Norman Kenneth A
Queen's University, Kingston, Canada.
Princeton University.
J Cogn Neurosci. 2017 Aug;29(8):1339-1354. doi: 10.1162/jocn_a_01132. Epub 2017 Apr 7.
Converging evidence supports the "nonmonotonic plasticity" hypothesis, which states 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 that 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 postreactivation 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, for example, in closed-loop experiments.
越来越多的证据支持“非单调可塑性”假说，该假说认为，虽然完整的回忆可能会强化记忆，但部分回忆会削弱记忆。然而，用于研究部分回忆效果的经典实验范式并不完全适合这样做，因为它们缺乏确保记忆被激活到适当程度所需的参数控制（即，存在一些回忆，但不足以导致记忆强化）。在此，我们提出了一种新颖的程序来满足这一需求。在参与者学习了一组单词-场景关联后，他们完成了一项线索心理可视化任务，该任务与多目标跟踪（MOT）程序相结合，我们选择该程序是因为它能够以参数可调节的方式干扰心理可视化（通过改变MOT目标的数量）。我们还使用功能磁共振成像（fMRI）数据成功训练了一个用于此任务的“联想回忆”分类器：该分类器显示，在参与者跟踪一个而不是五个MOT目标时提示联想记忆的试验中，记忆重新激活程度更高。然而，当没有发生回忆时，该分类器对任务难度不敏感，这表明它确实跟踪了记忆重新激活而不是任务难度本身。与分类器的结果一致，参与者对可视化生动性的内省评分受到MOT任务难度的调节。此外，我们在重新激活后的记忆测试中观察到分类器输出降低和反应减慢，这与MOT诱导的部分重新激活会削弱记忆的假说一致。这些结果作为一个“概念验证”，表明MOT可用于参数性地调节记忆检索——这一特性在未来对部分检索效果的研究中可能会很有用，例如在闭环实验中。
