Unstable foveation's impact on reading, object tracking, and its implications for diagnosing and intervening in reading difficulties.

Foveation, the ability to focus on a point for clear vision, is crucial for reading smoothly and tracking moving objects. Research shows that unstable foveation disrupts reading by causing more frequent eye movements. However, it's unclear if this also affects smooth tracking of moving targets in slow readers. This study therefore investigates the link between foveation during reading and the tracking of moving targets, in a large group of participants displaying variable reading speeds in a virtual reality environment. Our analysis shows that slower readers have more intrusive fixational eye movements characterized by greater spatial and temporal variability during reading. Additionally, these readers display less efficient tracking of moving targets. Interestingly, the rate and spatial variability of catch-up saccades during object tracking correlates with fixational eye movement rates and spatial variability during reading. Our findings thus demonstrate that poor foveation stability in slow readers also affects other eye movement activities, such as during object tracking. We conclude with a discussion on the limitations of virtual reality-based reading assessment and the shared mechanisms of foveal stabilization, which might be altered under conditions of reading impairment.