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Guanpeng Chen, Ziyun Zhu, Fang Fang; Offline transcranial direct current stimulation (tDCS) can improve the ability to perceive crowded targets. Journal of Vision 2019;19(10):65a. doi: https://doi.org/10.1167/19.10.65a.
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The deleterious influence of nearby flankers on target identification in the periphery is often referred to as visual crowding. Studying visual crowding can advance our understanding of the mechanisms of visual awareness and object recognition. Alleviating visual crowding (e.g., through perceptual learning) is one of the major ways to improve peripheral vision. Although there is a rapidly growing interest in using tDCS to modulate visual perception in humans, it remains unknown whether tDCS can alleviate visual crowding effects. We performed three experiments to investigate this issue. In Experiment 1, subjects were asked to perform an orientation discrimination task with the isolated and crowded targets in the periphery, before and after applying 20 minutes of 2 mA anodal tDCS to early visual cortex (P1 or P2) of the hemisphere contralateral or ipsilateral to the visual stimuli. We found that, electrical stimulation of the hemisphere contralateral to the visual stimuli could significantly reduce the crowding effect. This reduction was absent after the sham stimulation and could not be explained by the performance improvement with the isolated target. In Experiment 2, using the same behavioral task and the same tDCS protocol, we found that the contralateral DC stimulation remained effective in alleviating crowding at a smaller eccentricity. In Experiment 3, we adopted a letter recognition task and found that the alleviation of the letter crowding effect still existed after tDCS. In all the three experiments, no reduction was observed when tDCS was applied to the hemisphere ipsilateral to the visual stimuli. Taken together, we conclude that offline tDCS is effective in alleviating visual crowding across different visual eccentricities and perceptual tasks, which sheds new light on the mechanisms of visual crowding and possible practical applications.
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