Why have microsaccades become larger? Investigating eye deformations and detection algorithms

Area of Science:

• Ophthalmology
• Neuroscience
• Biomedical Engineering

Background:

• Reported microsaccade sizes have increased significantly since the 1950s-1960s.
• This increase may stem from modern eye-trackers measuring different ocular structures (e.g., pupil) than older techniques.

Purpose of the Study:

• To investigate if modern eye-tracking techniques contribute to larger reported microsaccade sizes.
• To explore how measuring different ocular structures impacts microsaccade analysis.
• To understand the effect of algorithmic signal processing on microsaccade measurements.

Main Methods:

• Experiment I: Recorded eye images during fixation, extracting movements of the pupil and Purkinje reflections.
• Experiment II: Compared microsaccade amplitudes computed by a common algorithm against human expert analysis.

Main Results:

• Different ocular structures yield distinct microsaccade signatures.
• Algorithmic detection resulted in larger microsaccade amplitudes than expert analysis, primarily due to unaddressed overshoots.
• Modern pupil-based trackers produce larger overshoots compared to historical systems.

Conclusions:

• Increased microsaccade amplitudes in recent studies are partly due to pupil overshoots from modern trackers.
• Lack of systematic algorithmic handling of overshoots contributes to amplitude discrepancies.
• Greater awareness of these dynamics is needed for standardized microsaccade definitions.