Visual cortex anodal tDCS does not alter reading performance for Chinese presented character-by-character to normal peripheral vision

Abstract

Visual cortex transcranial direct current stimulation (tDCS) reduces crowding in normal peripheral vision and may improve reading of English words in patients with macular degeneration. Given the different visual requirements of reading English words and Chinese characters, the effect of tDCS on peripheral reading performance in English might be different from Chinese. This study recruited seventeen participants (59 to 73 years of age) with normal vision and tested the hypothesis that anodal tDCS would improve reading of Chinese characters presented at 10° eccentricity compared with sham stimulation. Chinese sentences of different print sizes and exposure durations were presented one character at a time 10° below or to the left of fixation, and the individual critical print size (CPS) - the smallest print size eliciting the maximum reading speed (MRS) was determined. Reading accuracies for characters presented 0.2 logMAR smaller than the CPS were measured before, during, 5 mins, and 30 mins after receiving active or sham anodal visual cortex tDCS. Participants completed both the active and sham sessions in a random order following a double-blind, within-subject design. No effect of active anodal-tDCS on reading accuracy was observed, implying that a single session of tDCS did not improve Chinese character reading in normal peripheral vision. This may suggest that tDCS does not significantly reduce the crowding elicited within a single Chinese character. However, the effect of tDCS on between-character crowding is yet to be determined.