Battaglini Luca, Noventa Stefano, Casco Clara
Department of General Psychology, University of Padova, Via Venezia 8, 35131, Padova, Italy.
Hector Research Institute of Education Sciences and Psychology, Eberhard Karls Universität Tübingen, Tübingen, Germany.
Brain Stimul. 2017 Jul-Aug;10(4):773-779. doi: 10.1016/j.brs.2017.04.128. Epub 2017 Apr 28.
The effect that transcranial direct current stimulation (tDCS) has on discrimination of coherent motion (CM) signals in a field of randomly moving dots (noise) can be accounted for by both noise reduction and signal enhancement.
To distinguish between noise reduction and signal enhancement, we monitored the discrimination of the correct CM direction as a function of the coherence level (using the psychophysical method of constant stimuli). We then analyzed the threshold and slope parameters.
Thirty observers participated in the experiment; fifteen received cathodal stimulation, and fifteen received anodal stimulation, all over left V5.
The results showed that, rather than having opposite effects on CM discriminability, the positive- and negative-polarity tDCS over V5 affected the two parameters differently. When compared to a sham stimulation, anodal tDCS reduced the threshold, thus indicating signal enhancement. On the other hand, cathodal tDCS reduced the steepness of the slope (with better performance at low levels of coherence) compared to the sham stimulation, thus indicating noise reduction. Moreover, the results showed that late perceptual learning improved the participants' performance at medium/high CM similar to what anodal tDCS did.
These results suggest a dissociation between the neural mechanisms responsible for enhanced CM discriminability: reduction of noisy or uncorrelated motion by cathodal tDCS versus increased activation of weakly correlated motion signals by anodal tDCS or perceptual learning.
经颅直流电刺激（tDCS）对在随机移动点（噪声）场中相干运动（CM）信号辨别能力的影响可通过降噪和信号增强两种方式来解释。
为区分降噪和信号增强，我们监测了正确CM方向的辨别能力随相干水平的变化（采用恒定刺激的心理物理学方法）。然后分析了阈值和斜率参数。
30名观察者参与实验；15人接受阴极刺激，15人接受阳极刺激，均作用于左侧V5区。
结果表明，V5区的阳极和阴极tDCS对CM辨别能力并非产生相反影响，而是对两个参数的影响不同。与假刺激相比，阳极tDCS降低了阈值，表明信号增强。另一方面，与假刺激相比，阴极tDCS降低了斜率的陡度（在低相干水平下表现更好），表明降噪。此外，结果表明，晚期知觉学习改善了参与者在中/高CM时的表现，类似于阳极tDCS的作用。
这些结果表明，负责增强CM辨别能力的神经机制存在分离：阴极tDCS减少噪声或不相关运动，而阳极tDCS或知觉学习增加弱相关运动信号的激活。
