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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).
• Even very small displacements (0.1°) affected fixation durations, but effects varied by direction.
• Leftward and up-left shifts increased fixation durations, while downward shifts often shortened them.
• Saccade composition adapted: slightly fewer forward saccades and more regressions, concentrated on leftward shifts.
• Comprehension remained above chance, showing that readers compensated effectively despite visual instability.
• Findings support a direction-contingent tolerance model rather than a single global threshold.

Poster Summary

The ECVP 2025 poster (PDF) introduces 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 (18–39 years old).
• Method: Text displaced on each saccade by 0–0.53° in random directions.
• Results: ISDs changed fixation durations depending on direction, but saccade amplitudes and proportions were largely stable. Forward reading bias was preserved, though regressions increased in some conditions.
• Conclusion: ISDs disrupt alignment, but readers adapt dynamically, suggesting that costs reflect 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, but explained this as cancellation of opposing directional effects.
• Identified direction-specific costs: left and up-left displacements lengthen fixations; downward shifts shorten them; rightward shifts are near-neutral.
• Showed adaptive changes in saccade composition: fewer forward saccades, more regressions, and amplitude adjustments tuned to displacement geometry.
• Confirmed comprehension remained intact, meaning alignment errors increase oculomotor effort without preventing understanding.

Broader Impact

• Advances theoretical models (E-Z Reader, SWIFT) by introducing a prediction–match comparator stage.
• Explains clinical reading difficulties in conditions with eye movement instability (e.g. nystagmus, 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 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.