This study will be carried out in Ontario, Canada (University of Waterloo) and Hong Kong (The Hong Kong Polytechnic University). There are two conditions: Active brain stimulation + perceptual training and sham/placebo brain stimulation + perceptual training. This study uses a between-subjects design, such that half of all participants will be placed in the active stimulation group and half will be placed in the sham group.
Participants will be recruited from university-affiliated clinics and local clinical practices. Following full informed consent, participants will complete baseline testing and clinical testing to confirm that they meet eligibility criteria including: a diagnosis of macular degeneration without any additional eye disease, impaired vision but with enough visual acuity that the computer monitor can still present readable word, and no contraindications for brain stimulation interventions. Eligible participants will then be randomized to either receiving the active stimulation during perceptual training or the placebo stimulation during perceptual training.
The primary outcome measure is verbal reading accuracy for sentences presented on a computer screen following a Rapid Serial Visual Presentation (RSVP) task in which a single word is presented on the screen at a time. Participants will freely observe the words and will indicate the words on the screen verbally. The secondary outcome measures are contrast sensitivity and crowded and uncrowded visual acuity as measured by Freiburg Visual Acuity \& Contrast Test (FrACT) using the Landolt C stimulus. The "C"'s gap will be oriented randomly, and the participant will indicate the orientation of the stimulus. Crowded visual acuity will be assessed with Landolt C surrounded by a solid ring, while uncrowded visual acuity will be assessed with the Landolt C alone. The Test of contrast sensitivity will measure the amount of contrast required relative to the background to identify the orientation of the "C". The Hong Kong Polytechnic University has an additional set of secondary outcome measures of temporal and spatial visual span. Temporal visual span will be assessed using Chinese trigrams presented horizontally or vertically at the centre for a range of presentation times. Spatial visual span will be assessed using Chinese trigrams presented horizontally or vertically at different character positions for a fixed presentation time. Participants will be asked to recognize all three characters in a correct order.
The study consists of 9 sessions plus 1 additional session particularly for Hong Kong Polytechnic University
Session 0: This session only applies for The Hong Kong Polytechnic university, that horizontal and vertical temporal and spatial visual span will be collected.
Session 1: The first session will include the clinical evaluation. In addition, the pre tests of all outcome measures will be collected (RSVP performance, crowded and uncrowded visual acuity, contrast sensitivity).
Sessions 2-7: Brain stimulation sessions. Participants will undergo roughly 1 hour of perceptual training, performing the RSVP task. The first 25 minutes of this training will include either sham or active brain stimulation. A given participant will receive the same kind of stimulation for all 6 training sessions.
Session 8: No brain stimulation will occur. Post test outcome measures will be collected (RSVP performance, crowded and uncrowded visual acuity, contrast sensitivity, horizontal and vertical temporal and spatial visual span).
Session 9: 30 day follow up. 30 days after the final training session, participants will again perform the outcome measures without brain stimulation to determine the long term benefit of the perceptual training + brain stimulation.
