Developmental dyslexia is a common and serious specific learning disability affecting up to one in eight children in Hong Kong, with profound consequences for academic success and personal well-being. For children learning to read the visually complex Chinese script, the challenge is particularly intense. A key research challenge is a long-standing "chicken-and-egg" debate: are weaknesses in the brain's fast-processing visual system (Magnocellular-Dorsal deficits) a cause of reading difficulties, or merely a consequence of limited reading practice? This uncertainty has constrained theoretical progress, creating a major barrier to developing effective, evidence-based support for struggling readers beyond traditional linguistic-based methods.
This project is designed to resolve this debate by directly testing if training a core visual-attentional skill can causally improve reading. The approach is built on investigator's strong pilot data, which established a novel "Neurocognitive Cascade Model": a framework suggesting that the integrity of foundational visual processing impacts reading through a sequential chain reaction flowing from visual attention to working memory.
To test the model, investigators will employ a rigorous, assessor-blind randomized controlled trial with 100 Cantonese-speaking children with developmental dyslexia. Participants will be randomly assigned to either an intervention group that plays action video games, scientifically proven to enhance visual attention, or an active control group that plays a different type of non-action, engaging game. This design allows investigators to isolate the specific impact of the visual-attentional training. The investigators will track changes at four time points-before, during, immediately after the intervention, and at a 6-month follow-up-using a multi-level assessment battery, including objective neural signals of visual processing, cognitive skills, and real-world reading performance measured with advanced eye-tracking technology.
This research will deliver new knowledge that is both scientifically and socially impactful. It will provide the first causal evidence for a visual-attentional pathway to reading remediation in Chinese developmental dyslexia, fundamentally shifting theoretical understanding of the disorder from a single, phonological deficit to a more comprehensive, multi-component model. The findings will have a significant translational impact, paving the way for innovative, non-reading-based interventions and new early screening tools. Ultimately, this project will offer a new, evidence-based approach to help children overcome the specific neurocognitive bottlenecks that hinder their ability to learn to read, with the potential to improve educational outcomes for a large and underserved population.
Formal diagnosis of dyslexia by an educational or clinical psychologist using the Hong Kong Test of Specific Learning Difficulties in Reading and Writing (HKT-SpLD),39 with a literacy composite score at or below the 10th percentile.
Non-verbal IQ score ≥ 85 on Raven's Standard Progressive Matrices.
Normal or corrected-to-normal vision (both eyes logMAR 0.1 or better).
None
Factorial
Action video game intervention group
BehavioralParticipants will undergo 12 hours of training with a commercially available AVG (Rabbids: Party of Legends). This game is a direct successor to the Rayman Raving Rabbids game used in AVG intervention studies and shares its core mechanics. The game consists of numerous fast-paced mini-games in which players track multiple objects, respond to unpredictable events, and filter out distractions, thereby placing high demands on visual-spatial attention and attentional control.
Active Control (Non-Action Video Game) Group
BehavioralParticipants will undergo 12 hours of training with SimCity. To control for non-specific effects (e.g., gaming time, engagement, motivation), this group will play a non-action video game of matched duration and format. The investigators will use a commercially available city-building and management simulation game (e.g., SimCity), which is engaging and cognitively demanding (requiring planning and resource management). However, it critically lacks the fast, unpredictable, and attention-intensive elements of action games, ensuring that any observed group differences can be attributed specifically to the visual-attentional training provided by the AVG.
Visual Attention Span
Cued Number Identification Task: This task assesses the rapid deployment of visual attention. A string of five numbers (Geneva font, size 24, 98% contrast) is presented for 200 ms, followed by a 50-ms visual cue 1 cm beneath the target number. Numbers are spaced to subtend a 3.8° visual angle and minimise lateral masking. The child's task is to verbally report the cued number. The primary metric is the number of correctly reported targets out of 20 trials.
Verbal Backward Digit Span
An experimenter reads a sequence of numbers aloud (e.g., '8-2-5') and the child must mentally reverse the sequence and repeat it back ('5-2-8'). The sequence length progressively increases, placing increasing demands on both the storage and manipulation components of working memory. The score is the number of correctly recalled sequences.
Coherent Motion Detection
This task measures motion processing sensitivity using a random-dot kinematogram. Stimuli consist of 250 white dots (0.2° diameter; 50 cd/m²) moving at 0.24°/sec within a 5° circular aperture against a dark background (0.02 cd/m²). During each 400-ms trial, a percentage of 'signal' dots move coherently left or right. The task is to indicate the direct of the 'signal' dots.
Steady-State Visual Evoked Potentials (ssVEP)
Participants will view vertically oriented, sinusoidal gratings at 90% contrast. To target the magnocellular pathway, we will use low spatial frequency (SF) gratings of 0.6 cycles/degree, with high-SF gratings of 6.0 cycles/degree as a control. Both stimuli will phase-reverse at 7.5 Hz, generating a dominant 15 Hz ssVEP response. Although fully isolating the parvo- and magnocellular pathways is difficult, this combination of low spatial and high temporal frequency aims to produce a stronger activation of the magnocellular visual pathway.
Silent Reading and Eye Movement
Task: Participants will silently read 20 sentences constructed from age-appropriate, high-frequency Chinese characters (font: 'Free HK Kai', recommended by the Education Bureau). Each 18-character sentence spans two lines, with characters subtending a 2° visual angle. To ensure comprehension, a multiple-choice question will follow each sentence. Acquisition: Participants will be seated 50 cm from the screen with a forehead rest for stability. Eye movements will be recorded using a Tobii Pro Fusion eye-tracker (250 Hz sampling rate) following a successful nine-point calibration. Global Reading Metrics: Reading speed (characters per minute) and comprehension accuracy (%). Eye-Movement Metrics: Mean fixation duration, mean saccade length, and number of regressions
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