Rademaker Rosanne L, van de Ven Vincent G, Tong Frank, Sack Alexander T
Psychology Department, University of California San Diego, San Diego, California, United States of America.
Cognitive Neuroscience Department, Maastricht University, Maastricht, The Netherlands.
PLoS One. 2017 Apr 6;12(4):e0175230. doi: 10.1371/journal.pone.0175230. eCollection 2017.
Neuroimaging studies have demonstrated that activity patterns in early visual areas predict stimulus properties actively maintained in visual working memory. Yet, the mechanisms by which such information is represented remain largely unknown. In this study, observers remembered the orientations of 4 briefly presented gratings, one in each quadrant of the visual field. A 10Hz Transcranial Magnetic Stimulation (TMS) triplet was applied directly at stimulus offset, or midway through a 2-second delay, targeting early visual cortex corresponding retinotopically to a sample item in the lower hemifield. Memory for one of the four gratings was probed at random, and participants reported this orientation via method of adjustment. Recall errors were smaller when the visual field location targeted by TMS overlapped with that of the cued memory item, compared to errors for stimuli probed diagonally to TMS. This implied topographic storage of orientation information, and a memory-enhancing effect at the targeted location. Furthermore, early pulses impaired performance at all four locations, compared to late pulses. Next, response errors were fit empirically using a mixture model to characterize memory precision and guess rates. Memory was more precise for items proximal to the pulse location, irrespective of pulse timing. Guesses were more probable with early TMS pulses, regardless of stimulus location. Thus, while TMS administered at the offset of the stimulus array might disrupt early-phase consolidation in a non-topographic manner, TMS also boosts the precise representation of an item at its targeted retinotopic location, possibly by increasing attentional resources or by injecting a beneficial amount of noise.
神经影像学研究表明，早期视觉区域的活动模式能够预测在视觉工作记忆中被积极维持的刺激特性。然而，此类信息的表征机制在很大程度上仍不为人所知。在本研究中，观察者记住4个短暂呈现的光栅的方向，每个象限视野中各有一个。在刺激消失时，或者在2秒延迟的中途，直接施加10赫兹的经颅磁刺激（TMS）三联刺激，目标是与下半视野中的一个样本项目视网膜拓扑对应的早期视觉皮层。随机探测四个光栅之一的记忆，参与者通过调整方法报告该方向。与对角探测TMS刺激的错误相比，当TMS靶向的视野位置与提示的记忆项目的视野位置重叠时，回忆错误更小。这意味着方向信息的拓扑存储，以及在目标位置的记忆增强效应。此外，与晚期脉冲相比，早期脉冲在所有四个位置都会损害表现。接下来，使用混合模型对反应错误进行实证拟合，以表征记忆精度和猜测率。无论脉冲时间如何，靠近脉冲位置的项目的记忆更精确。无论刺激位置如何，早期TMS脉冲更可能出现猜测。因此，虽然在刺激阵列消失时施加的TMS可能以非拓扑方式破坏早期阶段的巩固，但TMS也可能通过增加注意力资源或注入适量有益噪声，在其目标视网膜拓扑位置增强项目的精确表征。
