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Rajkumar Nallour Raveendran, Katelyn Tsang, Dilraj Tiwana, Amy Chow, Ben Thompson; Anodal transcranial direct current stimulation reduces crowding in peripheral vision. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3307.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the effect of anodal transcranial direct stimulation (a-tDCS) on collinear lateral inhibition, a specific type of crowding, in normal peripheral vision. This is the first step towards studying the application of a-tDCS to visual rehabilitation in observers with central vision loss.
14 observers with normal vision [age:20-55 years; BCVA: 20/20 or better] performed a 2AFC lateral masking task, which involved staircase measurements of contrast detection thresholds for a target Gabor patch vertically flanked by two identical patches positioned at a distance of 2λ or 6λ. The stimuli were presented 6° to the left of a central fixation cross. Fixation was continuously monitored using an infrared eye tracker. Participants each completed two randomly sequenced stimulation sessions; real 0.2mA anodal tDCS of the primary visual cortex for 20 minutes and sham tDCS. Participants were masked to the type of stimulation. At each session, participants completed a block of four threshold measurements for each flanker distance pre-, during-, 5mins post- and 30mins post-stimulation.
The 2λ flanker separation elevated detection thresholds (inhibition/crowding) whereas the 6λ separation reduced thresholds (facilitation). A repeated measures ANOVA [2 stimulation types (active & sham) vs. 4-time periods (pre-, during-, 5mins post- and 30mins post-stimulation)] was conducted for each flanker separation distance separately. For the 2λ separation, a substantial reduction in detection threshold (reduced crowding) occurred during real but not sham a-tDCS [F(3,36)=2.95;p=0.045, post-hoc Tukey HSD pre- vs. during-stimulation (p=0.003) and pre- vs. 30min post-stimulation (p=0.004)]. No change in contrast threshold occurred for the 6λ separation condition during or after tDCS [F(3, 36)=0.46, p=0.72].
a-tDCS reduced collinear lateral inhibition/crowding in the normal periphery. This result is consistent with previous findings that a-tDCS transiently reduces inhibition within stimulated brain areas. Our results justify further exploration of the potential application of a-tDCS as a visual rehabilitation tool for individuals with central vision loss who are forced to rely on peripheral vision.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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