| Author: | Lyu, Anqi |
| Title: | Efficacy of interventions on improving Chinese reading performance in central vision loss |
| Advisors: | Cheong, Allen (SO) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Department: | School of Optometry |
| Pages: | xix, 176 pages : color illustrations |
| Language: | English |
| Abstract: | Reading serves as a crucial activity in preserving mental agility and fostering emotional health. It relies on high-resolution central vision and reading difficulty is a major concern for patients with central scotomas caused by macular degeneration, who are compelled to rely on para-central or peripheral retina for vision, known as the preferred retinal locus (PRL). Understanding the characteristics of the factors limiting peripheral reading performance could help develop effective visual rehabilitation for low-vision patients with central vision loss (CVL). Study I Introduction For English text, reduced visual span in both the temporal and spatial domains was correlated with a slower reading speed in peripheral vision. It is unknown whether the same is true for Chinese reading. Chinese consists of a vast number of characters that contain more visual information than individual English letters. Different visual faculties are required to recognize Chinese characters compared with those required for English. This distinction may impose different limitations on the visual span for reading Chinese in the periphery. Study I of this thesis examined the effect of visual span on reading Chinese characters in normal central and peripheral vision. Methods Twenty-six native Chinese readers (13 young and 13 older adults) were recruited. Reading performance in terms of maximum reading speed (MRS) and critical print size (CPS) was examined using the rapid serial visual presentation (RSVP) paradigm. Subjects were asked to read Chinese sentences presented character-by-character at three presentation locations: central vision, 10° left, and 10° below fixation. Temporal visual span was measured using trigrams of randomly selected Chinese characters presented at a range of exposure durations, while spatial visual span (SVS) was measured using trigrams presented at different spatial positions away from the fixation for 200 ms. Visual span measurements were made for all three visual field locations. Results Significantly faster RSVP MRS and smaller CPS were found at central vision compared with left and inferior visual fields (p < 0.001). No MRS or CPS difference was observed between the two peripheral locations. Visual span in terms of the temporal processing speed, average recognition accuracy at central five-character positions, and area under fitted SVS curves were better at central vision than at peripheral locations (p < 0.001). No difference in visual span was found between the left and inferior visual fields. Reading and visual span metrics were better in the young than older subjects (except for similar temporal processing speed at two peripheral locations). RSVP MRS was significantly correlated with temporal processing speed and spatial visual span for central and inferior visual fields (R2 > 0.18), but not at the left visual field. Conclusions The results for central and inferior presentation locations supported the hypothesis that visual span contributed to Chinese character reading speeds, imposing systematic impairments in Chinese reading at peripheral vision. Surprisingly, this hypothesis did not apply when read at 10° left of fixation, suggesting that factors affecting reading speed might differ for inferior and lateral peripheral viewing locations. Many rehabilitation approaches, including magnifiers, perceptual learning, and non-invasive brain stimulation, are available to alleviate these limitations and improve reading. Study II Introduction Anodal transcranial direct current stimulation (a-tDCS) is a form of non-invasive brain stimulation technique that enables the modulation of neural activity in superficial regions of human brain. When applied to the primary visual cortex, a-tDCS has been reported to reduce crowding in the peripheral vision, indicating its potential therapeutic use for reading rehabilitation. Study II of this thesis examined the acute effect of a single session of a-tDCS on improving the reading of Chinese characters presented to normal peripheral vision. Methods Seventeen older adults (59 to 73 years of age) with normal vision were recruited. Chinese sentences were presented one character at a time 10° to the left or below fixation at various speeds and print sizes using the RSVP method. MRS and CPS were determined using the same method adopted in Study I. Using a double-masked, within-subjects design, participants were tested with sentences of print size and presentation speed corresponding to 0.2 log MAR smaller than individually fitted CPS on two stimulation days, on which 20 mins of active or sham a-tDCS was applied to the visual cortex in a random order. Each test consisted of 15 sentences and one test was administered before, during, 5 mins, and 30 mins after the cessation of the stimulation. Reading accuracies were compared across time points. Results A within-subjects ANOVA revealed no significant interaction between stimulation type (active vs. sham) and time (pre, during, 5 mins, and 30 mins post-stimulation (F(3, 48) = 0.68, p = 0.57). Conclusions A single session of visual cortex a-tDCS did not improve the reading of Chinese characters in normal peripheral vision. The effect of a-tDCS on individuals with CVL is yet to be determined. Study III Introduction Generally, individuals with normal central vision are not familiar with using their peripheral vision for recognition or reading, which might potentially impact their learning capacity or the effectiveness of their rehabilitation. In contrast, patients with macular degeneration, in particular those with gradual disease progression, are more accustomed to relying on their peripheral retina for reading. It is possible that a stronger effect of a-tDCS on reading performance could be observed when patients read at their PRL. Study III of this thesis examined the acute effect of a single session of a-tDCS on improving Chinese reading performance in patients with CVL. Methods Thirteen patients diagnosed with macular degeneration (39 to 84 years of age) were recruited and their reading accuracies were compared before and after receiving active or sham a-tDCS using the same methodology as Study II. The only difference was that reading was assessed at patients’ habitual retinal location (e.g. PRL), instead of a fixed peripheral location. Results A within-subjects ANOVA revealed no significant interaction between stimulation type (active vs. sham) and time (pre, during, 5 mins, and 30 mins post-stimulation (F(3, 36) = 2.05, p = 0.12). Conclusions A single session of visual cortex a-tDCS did not improve the reading of Chinese characters in patients with CVL, prompting an inquiry into the efficacy of a single session of a-tDCS on improving Chinese reading performance, and if its impact could be enhanced when combined with perceptual learning. Study IV Introduction Perceptual learning, defined as changes in sensory function through repeated practice, can improve English reading speed in patients with CVL. Non-invasive brain stimulation, including a-tDCS, could enhance perceptual learning of visual tasks in individuals with normal or impaired vision. Study IV of this thesis examined the effect of combined multiple sessions of a-tDCS and perceptual learning on improving Chinese reading performance in patients with CVL. Methods This study employed a between-subjects, double-masked, randomized, placebo-controlled design. Twenty patients diagnosed with macular degeneration (39 to 90 years of age) were recruited and randomly assigned to either an experimental group receiving active a-tDCS, or a control group receiving sham a-tDCS. Both groups underwent six sessions of a-tDCS combined with RSVP reading training over three weeks. Character reading performance was assessed using the RSVP method and text reading performance was assessed using the Chinese version of MNRead Acuity Charts. RSVP MRS and text reading speed were compared before, one day after, and one month after all training sessions. Results Both groups of patients showed significant RSVP MRS improvements at 1-day and 1-month post-training (F(1, 18) = 2.22, p < 0.001). No difference was found between the 2 post-tests (p > 0.99). No difference in the magnitude of the improvements was found between the two groups, despite multiple sessions of a-tDCS being administered (F(2, 36) = 0.01, p = 0.99). Text reading speed did not change after the training (F(2, 36) = 0.15, p = 0.86). Conclusions Six sessions of RSVP training increased Chinese character reading speed in patients with CVL, and the improvement lasted for at least one month. However, a-tDCS did not result in enhanced RSVP-based perceptual learning in CVL patients when they read Chinese. Because real-world Chinese reading involves multiple characters presented together, future studies should use reading materials that present sentences or text to explore the impact of a-tDCS on replicating real-world reading experiences. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13075