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Experiment Simulation

Watch a short demonstration of the saccade-contingent displacement paradigm used in this research.

Cliff Notes

• Reading depends on stable spatial representations across saccades.
• This research imposed intra-saccadic displacements (ISDs) of text (0–20 px / up to 0.53° / ~2 letters).
• Very small displacements around 0.1° affected fixation durations, with effects varying by direction.
• Leftward and up-left shifts increased fixation durations, while downward shifts often shortened them.
• Saccade composition adapted, with slightly fewer forward saccades and more regressions, concentrated on leftward shifts.
• Comprehension remained above chance, indicating effective compensation despite visual instability.
• Findings support a direction-contingent tolerance model rather than a single global threshold.

Poster Summary

The ECVP 2025 poster (PDF) introduced the idea that reading relies on world-centred as well as gaze-centred representations. By shifting entire paragraphs during saccades, the study tested how readers track text when predictions and actual input diverge.

• Participants: 19 fluent English speakers aged 18–39 years.
• Method: Text was displaced on each saccade by 0–0.53° in random directions.
• Results: ISDs changed fixation durations depending on direction, while saccade amplitudes and proportions were largely stable. Forward reading bias was preserved, though regressions increased in some conditions.
• Conclusion: ISDs disrupted alignment, but readers adapted dynamically, suggesting that costs reflected alignment effort rather than wholesale processing breakdown.

Thesis Overview

The thesis (Impact of Intra-Saccadic Displacements on Reading Performance) provides the full experimental framework and in-depth statistical analysis.

Main Contributions

• Demonstrated a shallow inverted-U profile for pooled fixation durations, peaking around 0.30 characters, explained as cancellation of opposing directional effects.
• Identified direction-specific costs: left and up-left displacements lengthened fixations, downward shifts shortened them, rightward shifts were near-neutral.
• Showed adaptive changes in saccade composition, with fewer forward saccades, more regressions, and amplitude adjustments tuned to displacement geometry.
• Confirmed that comprehension remained intact, indicating that alignment errors increased oculomotor effort without preventing understanding.

Broader Impact

• Advances theoretical models such as E-Z Reader and SWIFT by introducing a prediction–match comparator stage.
• Explains clinical reading difficulties in conditions with eye movement instability such as nystagmus and oscillopsia.
• Guides the design of assistive displays and adaptive typography that minimise costly displacement directions.

Overall Research Contribution

This programme of research unifies experimental, computational, and clinical perspectives on how readers cope with spatial instability. The results show that:

• Readers tolerate small prediction errors through alignment-based remapping.
• Costs scale with the direction and geometry of displacement, not simply with size.
• Behavioural adaptation involves redistributing saccades rather than uniformly slowing down fixations.
• Understanding this tolerance function can inform both reading models and rehabilitation strategies.