Reduced perceptual span in dyslexic children: a gaze-contingent eye-tracking study

In typically developing 9-year-olds, the perceptual span-the region of text from which useful information is extracted during a single eye fixation-extends up to seven characters to the right of fixation. This parafoveal preview supports fluent reading by facilitating saccade planning and lexical preprocessing. However, the perceptual span in children with dyslexia remains undocumented, and findings in adults are inconsistent. While theoretical models suggest a reduced span in dyslexia, this study offers the first experimental test of this hypothesis in children.

14 dyslexic children aged 9- to 12-year-old and 24 age-matched controls participated in the present eye-tracking study. Using a gaze-contingent window paradigm, children read sentences aloud while the number of visible characters around the point of fixation was systematically manipulated. Reading speed, reading accuracy, fixation duration and saccade length were assessed across five window size conditions.

Our results show a diminished impact of window sizes on the reading speed of children with dyslexia as compared to controls. Eye-tracking data confirmed an increased foveal load and reduced parafoveal processing for this group. In both groups, gaze-contingent windows did not impact reading accuracy.

Results are interpreted within the framework of the foveal load hypothesis, alongside prior evidence of reduced preview benefit and heightened visual crowding in dyslexia. In this view, the greater effort required for foveal word identification in dyslexic readers limits the attentional resources available for parafoveal processing, thereby constraining access to upcoming text and ultimately reducing the effective perceptual span during reading.