Department of General Psychology, University of Padova, Padova, Italy.
Neuro.Vis.U.S. Laboratory, University of Padova, Padova, Italy.
Restor Neurol Neurosci. 2020;38(5):395-405. doi: 10.3233/RNN-201050.
To study motion perception, a stimulus consisting of a field of small, moving dots is often used. Generally, some of the dots coherently move in the same direction (signal) while the rest move randomly (noise). A percept of global coherent motion (CM) results when many different local motion signals are combined. CM computation is a complex process that requires the integrity of the middle-temporal area (MT/V5) and there is evidence that increasing the number of dots presented in the stimulus makes such computation more efficient.
In this study, we explored whether anodal direct current stimulation (tDCS) over MT/V5 would increase individual performance in a CM task at a low signal-to-noise ratio (SNR, i.e. low percentage of coherent dots) and with a target consisting of a large number of moving dots (high dot numerosity, e.g. >250 dots) with respect to low dot numerosity (<60 dots), indicating that tDCS favour the integration of local motion signal into a single global percept (global motion).
Participants were asked to perform a CM detection task (two-interval forced-choice, 2IFC) while they received anodal, cathodal, or sham stimulation on three different days.
Our findings showed no effect of cathodal tDCS with respect to the sham condition. Instead, anodal tDCS improves performance, but mostly when dot numerosity is high (>400 dots) to promote efficient global motion processing.
The present study suggests that tDCS may be used under appropriate stimulus conditions (low SNR and high dot numerosity) to boost the global motion processing efficiency, and may be useful to empower clinical protocols to treat visual deficits.
为了研究运动感知，通常使用由小运动点组成的刺激。通常，一些点一致地朝着相同的方向（信号）运动，而其余的点随机运动（噪声）。当许多不同的局部运动信号组合在一起时，会产生整体一致运动（CM）的感知。CM 计算是一个复杂的过程，需要中颞区（MT/V5）的完整性，并且有证据表明，增加刺激中呈现的点的数量可以使这种计算更有效。
在这项研究中，我们探讨了 MT/V5 的阳极直流电刺激（tDCS）是否会在低信噪比（SNR，即低比例的一致点）和大数量的运动点（高点数，例如>250 个点）的 CM 任务中提高个体的表现，相对于低点数（<60 个点），表明 tDCS 有利于将局部运动信号整合为单一的整体感知（全局运动）。
参与者在三天的时间内分别接受阳极、阴极或假刺激，然后要求他们完成 CM 检测任务（两间隔强制选择，2IFC）。
我们的研究结果显示，与假刺激相比，阴极 tDCS 没有效果。相反，阳极 tDCS 可以提高表现，但主要是在点数高（>400 个点）时，以促进有效的全局运动处理。
本研究表明，tDCS 可在适当的刺激条件下（低 SNR 和高点数）用于提高全局运动处理效率，可能有助于加强治疗视觉缺陷的临床方案。
