Transcranial Direct Current Stimulation Does Not Enhance Perceptual Learning of Chinese Character Reading in Adults With Macular Degeneration

Purpose: Macular degeneration impairs central vision, compelling patients to use their peripheral vision for reading, which is difficult due to reduced spatial resolution and crowding. Although perceptual learning improves reading, single-session anodal transcranial direct current stimulation (a-tDCS) over the visual cortex has shown inconsistent outcomes, with transient improvements observed in English reading but no benefit for Chinese reading in macular degeneration patients. This randomized controlled trial investigated whether combining multi-session a-tDCS with perceptual learning enhances Chinese reading performance in these patients compared to sham stimulation. Methods: Twenty Chinese-reading patients with macular degeneration (39-90 years old) were randomized to receive either active (n = 10) or sham (n = 10) a-tDCS during six sessions of rapid serial visual presentation (RSVP) reading training. Trained outcomes (RSVP reading) and untrained functions (sentence reading, crowding, contrast sensitivity, and visual acuity) were compared at baseline, 1 day, and 1 month post-training. Results: Perceptual learning significantly improved RSVP reading speed (P < 0.001) in both groups, with effects lasting at least a month. No additive effect of active versus sham a-tDCS was observed (group × time P = 0.99). Transfer effects to untrained functions were limited to visual acuity and critical print size for sentence reading. Conclusions: Perceptual learning enhances Chinese reading performance in individuals with macular degeneration, but a-tDCS confers no additional benefit. This contrasts with previous results where non-invasive brain stimulation enhanced English reading in macular degeneration. The results emphasize the need for more refined neuromodulation strategies for improving logographic reading.