Abstract
Purpose :
While reading text with peripheral vision is difficult, it becomes necessary when central vision is impaired due to macular degeneration. In two within-subject, double-blind, placebo-controlled experiments testing participants with normal vision, we investigated whether two different non-invasive transcranial electrical stimulation (tES) protocols targeting early visual areas can improve peripheral reading ability.
Methods :
All procedures were identical across both experiments, except that Exp 1 (N = 10) used transcranial random noise stimulation (tRNS: 2mA peak to peak, 20 min, 30 sec ramps) applied bilaterally to early visual areas and Exp 2 (N = 10) used transcranial direct current stimulation (tDCS: 2mA, 20 min, 30 sec ramps), with the anode on the occipital pole and the cathode on a cheek. Each experiment comprised an active tES session and a placebo tES session, randomly ordered. On each stimulation session, participants performed a 15-sentence reading test before tES (pre-test), during tES (during), 5 min after tES (post5), and 30 min after tES (post30). Sentences were presented 10 degrees below fixation, one word at a time. Participants read each sentence aloud, and fixation was verified with eye tracking. Accuracy was calculated as the proportion of words read correctly, and the effect of tES was quantified as the accuracy difference between pre-test and each of the post-tests.
Results :
Active tRNS induced a significantly greater improvement than placebo, F(1,9) = 19.6, p = 0.002 (active improvement: 4.8% ± 2.1, placebo improvement: 0.5% ± 1.4). In contrast, active tDCS did not differ from placebo (active: 4.0% ± 1.5, placebo: 4.9% ± 1.4).
Conclusions :
TRNS improved peripheral reading, but tDCS did not. TRNS may have delivered more effective excitatory neuromodulation to the relatively deep cortical area supporting 10-degree eccentric vision. The tRNS effect may also benefit from delivering excitatory stimulation with both electrodes. Although additional work must clarify the factors that influence the effectiveness of different stimulation protocols, tRNS may be generally useful for improving peripheral reading.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.