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Latifa Lazzouni, Dave Saint-Amour; Modulation of orientation discrimination in artificial scotoma zone with transcranial direct current stimulation. Journal of Vision 2014;14(10):54. doi: 10.1167/14.10.54.
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© ARVO (1962-2015); The Authors (2016-present)
When looking at a dynamic texture, a circumscribed lack of visual information in the peripheral visual field tends to be filled with the surrounding pattern, a phenomenon that is associated with visual completion or filling-in of the artificial scotoma. The underlying mechanisms are thought to involve disinhibition, which yields to invading activity of hyper-excited neighbouring neurons into the deafferented area (scotoma). The present study took advantage of this phenomenon to investigate short-term plasticity in the human visual system. We first aimed to investigate the strength of the filling-in effect of a peripheral artificial scotoma by measuring orientation discrimination thresholds. Second, transcranial direct current stimulation (tDCS) was used to modulate filling-in effects by changing visual cortex excitability. Thirteen healthy participants (with normal or corrected vision) took part in the study. In the psychophysical experiment, 6 subjects had to decide whether a Gabor patch presented in the scotoma zone was tilted to the left or to the right from the vertical, under two conditions: the filling-in (conditioning) and control (no-conditioning) conditions. Orientation thresholds were obtained using a 1-up/2-down staircase procedure, and compared using t-tests. In the tDCS experiment (n=7) the task was repeated, but under online tDCS over Oz, either with anodal or sham. Both sessions were separated by at least 48 hours. A repeated-measure ANOVA was performed with factors Task (conditioning vs. no-conditioning) and Stimulation (anodal vs. sham). Results show a significant main effect of Task, such that thresholds during conditioning were higher than the control task, and this effect was increased by the anodal stimulation with a significant interaction between both factors. These preliminary results show that the filling-in of an artificial scotoma increases subsequent orientation thresholds in the inner scotoma zone. This filling-in effect, which is likely due to disinhibition and invading activity, can be influenced with tDCS.
Meeting abstract presented at VSS 2014
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